rounding different in order to original quote calculation

[fooman]

When retrieving calculatedTaxes here

https://github.com/magento/magento2/blob/master/app/code/Magento/Tax/Helper/Data.php#L897

$taxClassAmount[$taxClassId]['tax_amount']      += $price * $percent / 100;

the amounts are not rounded leading to different results to the original quote calculation.

Magento should be able to reconstruct the complete taxation on the order and produce the same results as the original quote (irrespective of any setting changes).

[verklov]

Hello fooman,
Thank you for reporting this issue! We are considering to apply a bunch of fixes related to tax calculation. The issue reported by you will most likely be fixed by one of them. So far we are leaving the issue open and will close it once it is fixed by one of the future code updates.

[verklov]

Hello fooman,
Could you please provide us with the steps how we can reproduce this issue and see the difference in the results because of the rounding issue you reported?

[fooman]

The code is clearly different:

$taxClassAmount[$taxClassId]['tax_amount']      += $price * $percent / 100;

compared to

/**
* Calculate address tax amount based on one unit price and tax amount
*
* @param \Magento\Sales\Model\Quote\Address $address
* @return \Magento\Tax\Model\Sales\Total\Quote\Tax
*/
protected function _unitBaseCalculation(\Magento\Sales\Model\Quote\Address $address, $taxRateRequest)
{
    $items = $this->_getAddressItems($address);
    $itemTaxGroups = array();
    foreach ($items as $item) {
        if ($item->getParentItem()) {
            continue;
        }

        if ($item->getHasChildren() && $item->isChildrenCalculated()) {
            foreach ($item->getChildren() as $child) {
                $taxRateRequest->setProductClassId($child->getProduct()->getTaxClassId());
                $rate = $this->_calculator->getRate($taxRateRequest);
                $this->_calcUnitTaxAmount($child, $rate);
                $this->_addAmount($child->getTaxAmount());
                $this->_addBaseAmount($child->getBaseTaxAmount());
                $applied = $this->_calculator->getAppliedRates($taxRateRequest);
                if ($rate > 0) {
                    $itemTaxGroups[$child->getId()] = $applied;
                }
                $this->_saveAppliedTaxes(
                    $address,
                    $applied,
                    $child->getTaxAmount(),
                    $child->getBaseTaxAmount(),
                    $rate
                );
                $child->setTaxRates($applied);
            }
            $this->_recalculateParent($item);
        }
        else {
            $taxRateRequest->setProductClassId($item->getProduct()->getTaxClassId());
            $rate = $this->_calculator->getRate($taxRateRequest);
            $this->_calcUnitTaxAmount($item, $rate);
            $this->_addAmount($item->getTaxAmount());
            $this->_addBaseAmount($item->getBaseTaxAmount());
            $applied = $this->_calculator->getAppliedRates($taxRateRequest);
            if ($rate > 0) {
                $itemTaxGroups[$item->getId()] = $applied;
            }
            $this->_saveAppliedTaxes(
                $address,
                $applied,
                $item->getTaxAmount(),
                $item->getBaseTaxAmount(),
                $rate
            );
            $item->setTaxRates($applied);
        }
    }
    if ($address->getQuote()->getTaxesForItems()) {
        $itemTaxGroups += $address->getQuote()->getTaxesForItems();
    }
    $address->getQuote()->setTaxesForItems($itemTaxGroups);
    return $this;
}

/**
* Calculate unit tax anount based on unit price
*
* @param \Magento\Sales\Model\Quote\Item\AbstractItem $item
* @param float $rate
* @return \Magento\Tax\Model\Sales\Total\Quote\Tax
*/
protected function _calcUnitTaxAmount(\Magento\Sales\Model\Quote\Item\AbstractItem $item, $rate)
{
    $qty = $item->getTotalQty();
    $inclTax = $item->getIsPriceInclTax();
    $price = $item->getTaxableAmount() + $item->getExtraTaxableAmount();
    $basePrice = $item->getBaseTaxableAmount() + $item->getBaseExtraTaxableAmount();
    $rateKey = (string)$rate;
    $item->setTaxPercent($rate);

    $hiddenTax = null;
    $baseHiddenTax = null;
    switch ($this->_config->getCalculationSequence($this->_store)) {
        case \Magento\Tax\Model\Calculation::CALC_TAX_BEFORE_DISCOUNT_ON_EXCL:
        case \Magento\Tax\Model\Calculation::CALC_TAX_BEFORE_DISCOUNT_ON_INCL:
            $unitTax = $this->_calculator->calcTaxAmount($price, $rate, $inclTax);
            $baseUnitTax = $this->_calculator->calcTaxAmount($basePrice, $rate, $inclTax);
            break;
        case \Magento\Tax\Model\Calculation::CALC_TAX_AFTER_DISCOUNT_ON_EXCL:
        case \Magento\Tax\Model\Calculation::CALC_TAX_AFTER_DISCOUNT_ON_INCL:
            $discountAmount = $item->getDiscountAmount() / $qty;
            $baseDiscountAmount = $item->getBaseDiscountAmount() / $qty;

            $unitTax = $this->_calculator->calcTaxAmount($price, $rate, $inclTax);
            $discountRate = ($unitTax/$price) * 100;
            $unitTaxDiscount = $this->_calculator->calcTaxAmount($discountAmount, $discountRate, $inclTax, false);
            $unitTax = max($unitTax - $unitTaxDiscount, 0);
            $baseUnitTax = $this->_calculator->calcTaxAmount($basePrice, $rate, $inclTax);
            $baseDiscountRate = ($baseUnitTax/$basePrice) * 100;
            $baseUnitTaxDiscount = $this->_calculator
                ->calcTaxAmount($baseDiscountAmount, $baseDiscountRate, $inclTax, false);
            $baseUnitTax = max($baseUnitTax - $baseUnitTaxDiscount, 0);

            if ($inclTax && $discountAmount > 0) {
                $hiddenTax = $this->_calculator->calcTaxAmount($discountAmount, $rate, $inclTax, false);
                $baseHiddenTax = $this->_calculator->calcTaxAmount($baseDiscountAmount, $rate, $inclTax, false);
                $this->_hiddenTaxes[] = array(
                    'rate_key' => $rateKey,
                    'qty' => $qty,
                    'item' => $item,
                    'value' => $hiddenTax,
                    'base_value' => $baseHiddenTax,
                    'incl_tax' => $inclTax,
                );
            } elseif ($discountAmount > $price) { // case with 100% discount on price incl. tax
                $hiddenTax = $discountAmount - $price;
                $baseHiddenTax = $baseDiscountAmount - $basePrice;
                $this->_hiddenTaxes[] = array(
                    'rate_key' => $rateKey,
                    'qty' => $qty,
                    'item' => $item,
                    'value' => $hiddenTax,
                    'base_value' => $baseHiddenTax,
                    'incl_tax' => $inclTax,
                );
            }
            break;
    }
    $item->setTaxAmount($this->_store->roundPrice(max(0, $qty*$unitTax)));
    $item->setBaseTaxAmount($this->_store->roundPrice(max(0, $qty*$baseUnitTax)));

    return $this;
}

/**
* Calculate address total tax based on row total
*
* @param \Magento\Sales\Model\Quote\Address $address
* @param \Magento\Object $taxRateRequest
* @return \Magento\Tax\Model\Sales\Total\Quote\Tax
*/
protected function _rowBaseCalculation(\Magento\Sales\Model\Quote\Address $address, $taxRateRequest)
{
    $items = $this->_getAddressItems($address);
    $itemTaxGroups = array();
    foreach ($items as $item) {
        if ($item->getParentItem()) {
            continue;
        }
        if ($item->getHasChildren() && $item->isChildrenCalculated()) {
            foreach ($item->getChildren() as $child) {
                $taxRateRequest->setProductClassId($child->getProduct()->getTaxClassId());
                $rate = $this->_calculator->getRate($taxRateRequest);
                $this->_calcRowTaxAmount($child, $rate);
                $this->_addAmount($child->getTaxAmount());
                $this->_addBaseAmount($child->getBaseTaxAmount());
                $applied = $this->_calculator->getAppliedRates($taxRateRequest);
                if ($rate > 0) {
                    $itemTaxGroups[$child->getId()] = $applied;
                }
                $this->_saveAppliedTaxes(
                    $address,
                    $applied,
                    $child->getTaxAmount(),
                    $child->getBaseTaxAmount(),
                    $rate
                );
                $child->setTaxRates($applied);
            }
            $this->_recalculateParent($item);
        }
        else {
            $taxRateRequest->setProductClassId($item->getProduct()->getTaxClassId());
            $rate = $this->_calculator->getRate($taxRateRequest);
            $this->_calcRowTaxAmount($item, $rate);
            $this->_addAmount($item->getTaxAmount());
            $this->_addBaseAmount($item->getBaseTaxAmount());
            $applied = $this->_calculator->getAppliedRates($taxRateRequest);
            if ($rate > 0) {
                $itemTaxGroups[$item->getId()] = $applied;
            }
            $this->_saveAppliedTaxes(
                $address,
                $applied,
                $item->getTaxAmount(),
                $item->getBaseTaxAmount(),
                $rate
            );
            $item->setTaxRates($applied);
        }
    }

    if ($address->getQuote()->getTaxesForItems()) {
        $itemTaxGroups += $address->getQuote()->getTaxesForItems();
    }
    $address->getQuote()->setTaxesForItems($itemTaxGroups);
    return $this;
}

/**
* Calculate item tax amount based on row total
*
* @param \Magento\Sales\Model\Quote\Item\AbstractItem $item
* @param float $rate
* @return \Magento\Tax\Model\Sales\Total\Quote\Tax
*/
protected function _calcRowTaxAmount($item, $rate)
{
    $inclTax = $item->getIsPriceInclTax();
    $subtotal = $item->getTaxableAmount() + $item->getExtraRowTaxableAmount();
    $baseSubtotal = $item->getBaseTaxableAmount() + $item->getBaseExtraRowTaxableAmount();
    $rateKey = (string)$rate;
    $item->setTaxPercent($rate);

    $hiddenTax = null;
    $baseHiddenTax = null;
    switch ($this->_taxData->getCalculationSequence($this->_store)) {
        case \Magento\Tax\Model\Calculation::CALC_TAX_BEFORE_DISCOUNT_ON_EXCL:
        case \Magento\Tax\Model\Calculation::CALC_TAX_BEFORE_DISCOUNT_ON_INCL:
            $rowTax = $this->_calculator->calcTaxAmount($subtotal, $rate, $inclTax);
            $baseRowTax = $this->_calculator->calcTaxAmount($baseSubtotal, $rate, $inclTax);
            break;
        case \Magento\Tax\Model\Calculation::CALC_TAX_AFTER_DISCOUNT_ON_EXCL:
        case \Magento\Tax\Model\Calculation::CALC_TAX_AFTER_DISCOUNT_ON_INCL:
            $discountAmount = $item->getDiscountAmount();
            $baseDiscountAmount = $item->getBaseDiscountAmount();
            $rowTax = $this->_calculator->calcTaxAmount(
                max($subtotal - $discountAmount, 0),
                $rate,
                $inclTax
            );
            $baseRowTax = $this->_calculator->calcTaxAmount(
                max($baseSubtotal - $baseDiscountAmount, 0),
                $rate,
                $inclTax
            );
            if ($inclTax && $discountAmount > 0) {
                $hiddenTax = $this->_calculator->calcTaxAmount($discountAmount, $rate, $inclTax, false);
                $baseHiddenTax = $this->_calculator->calcTaxAmount($baseDiscountAmount, $rate, $inclTax, false);
                $this->_hiddenTaxes[] = array(
                    'rate_key' => $rateKey,
                    'qty' => 1,
                    'item' => $item,
                    'value' => $hiddenTax,
                    'base_value' => $baseHiddenTax,
                    'incl_tax' => $inclTax,
                );
            } elseif ($discountAmount > $subtotal) { // case with 100% discount on price incl. tax
                $hiddenTax = $discountAmount - $subtotal;
                $baseHiddenTax = $baseDiscountAmount - $baseSubtotal;
                $this->_hiddenTaxes[] = array(
                    'rate_key' => $rateKey,
                    'qty' => 1,
                    'item' => $item,
                    'value' => $hiddenTax,
                    'base_value' => $baseHiddenTax,
                    'incl_tax' => $inclTax,
                );
            }
            break;
    }
    $item->setTaxAmount(max(0, $rowTax));
    $item->setBaseTaxAmount(max(0, $baseRowTax));
    return $this;
}

[choukalos]

The tax calculation was changed extensively in 1.x branch. Those changes will be ported to 2x as part of our current roadmap. I'm closing this issue for now as I believe this will be resolved when the tax calculation changes from 1.x are ported.

[fooman]

The above comment is true for Magento 1.8.1 and Magento 2 - I don't consider this fixed yet.

[verklov]

@fooman, the team processed this issue. The fix has just been released with version 0.1.0-alpha94. Please verify the latest code available.

[seansan]

Was this bug also fixed in m1? or is there a solution somewhere?