How To: Increase the Accuracy of Tax, Discount, and Total Value Calculation

By default, CS-Cart rounds decimals to 2 decimal places. If a customer buys a large number of products, and product price or tax rate value has 2 decimal places, it may lead to inaccuracy in the nearest tenth or hundredth of tax, discount, and total value calculation.

You can increase the calculation accuracy in 2 steps.

Important

Your Tax calculation method based on setting under Settings → General must be set to Subtotal for the second step to work properly.

If your tax calculation method is based on Unit price, you only need to complete Step 1 to get the increased calculation accuracy, but then PayPal payment methods will not work in your shop.

Step 1. Modify fn.common.php

1.1. Open the fn.common.php file located in the app/functions directory of your CS-Cart installation.

1.2. Find this line of the code:

$price = sprintf('%.' . $decimals . 'f', round((double) $price + 0.00000000001, $decimals));

1.3. Replace this line with one of the following lines, depending on the value of the Tax calculation method based on setting under Settings → General:

  • For Subtotal, use this line:

    $price = sprintf('%.' . $decimals . 'f', round((double) $price + 0.00000000001, 4));

  • For Unit price, use this line:

    $price = sprintf('%.' . 4 . 'f', round((double) $price + 0.00000000001, 4));

1.4. Save the file. This will make CS-Cart round decimals to 4 digits.

Note

You can set any number of digits after decimal point by replacing 4 with the number you want.

Step 2. Additional Changes for PayPal Users

PayPal only supports xx.xx (2 decimal places) price format. If you want to increase the calculation accuracy and use a PayPal payment method, make the following changes:

Important

The changes below will work only if you set your Tax calculation method based on setting under Settings → General to Subtotal and modify the fn.common.php file as described in Step 1.

2.1. Open the fn.common.php file located in the app/functions directory of your CS-Cart installation

2.2. Add the following piece of the code to the end of the file:

function fn_format_price_paypal($price = 0)
{
     return sprintf("%.2f", round((double) $price + 0.00000000001, 2));
}
function fn_format_price_by_currency_paypal($price, $currency_from = CART_PRIMARY_CURRENCY, $currency_to = CART_SECONDARY_CURRENCY)
{
    $currencies = Registry::get('currencies');
    $currency_from = $currencies[$currency_from];
    $currency_to = $currencies[$currency_to];

    $result = fn_format_price_paypal($price / ($currency_to['coefficient'] / $currency_from['coefficient']), CART_SECONDARY_CURRENCY);

    /**
     * Update converted value
     *
     * @param float  $price         value to be converted
     * @param string $currency_from in what currency did we get the value
     * @param string $currency_to   in what currency should we send the result
     * @param float  $result        converted value
     */
    fn_set_hook('format_price_by_currency_paypal_post', $price, $currency_from, $currency_to, $result);

    return $result;
}

2.3. Save the file.

2.4. Open the paypal.php file in the app/addons/paypal/payments directory of your CS-Cart installation.

2.5. Change the following line:

Find this line: $paypal_shipping = fn_order_shipping_cost($order_info);
Replace it with: $paypal_shipping = fn_format_price_paypal(fn_order_shipping_cost($order_info));

2.6. Replace all instances of fn_format_price with fn_format_price_paypal:

Find this code: fn_format_price(
Replace it with: fn_format_price_paypal(

2.7. Replace all instances of fn_format_price_by_currency with fn_format_price_by_currency_paypal:

Find this code: fn_format_price_by_currency(
Replace it with: fn_format_price_by_currency_paypal(

2.8. Save the file.

2.9. Complete the steps below for all the .php files in the app/addons/paypal/payments directory of your CS-Cart installation:

  • Open the file.

  • Replace all instances of fn_format_price with fn_format_price_paypal:

    Find this code: fn_format_price(
    Replace it with: fn_format_price_paypal(

  • Replace all instances of fn_format_price_by_currency with fn_format_price_by_currency_paypal:

    Find this code: fn_format_price_by_currency(
    Replace it with: fn_format_price_by_currency_paypal(

  • Save the file.