public static function calculateTaxClass($amountInclTax, $taxAmount)
    {
        $taxClasses = array(
            0 => 'N',
            9 => 'L',
            21 => 'H'
        );

        $taxRate = self::calculateTaxPercentage($amountInclTax, $taxAmount);

        $nearestTaxRate = self::nearest($taxRate, array_keys($taxClasses));
        return $taxClasses[$nearestTaxRate];
    }