public function getTotalTaxAmount()
    {
        // Convert to minor units for more accurate calculations
        $total_amount = CurrencyUtils::amountToExponent($this->getTotalAmount(), $this->currency);
        $tax_rate     = CurrencyUtils::amountToExponent($this->tax_rate, $this->currency);

        $total_tax_amount = ceil(
            $total_amount - ( ($total_amount * 10000) / (10000 + $tax_rate) )
        );

        return CurrencyUtils::exponentToAmount($total_tax_amount, $this->currency);
    }