Rounding Error in Total Price Calculation

[jochemschulten]

The issue arises from rounding during the calculation of the exclusive price in the cleanExclusive function of the InclusiveAccuracyFix trait.

Example:

• Product price: 15.00€ (Including 21% VAT)
• Quantity: 12
• The total is shown as: € 180.05, but it should be € 180.04.

Explanation:

The rounding happens when the exclusive price is calculated in the cleanExclusive function. Here's the problem:

1. The product price of € 15.00 (including 21% VAT) is divided by 1 + ($factor / 100) to get the price excluding VAT:

   • In the case of 21% VAT, the calculation is € 15.00 / 1.21 = € 12.3966942.

2. However, the result is rounded using RoundingMode::HALF_UP, which causes the price to be rounded to 12.40€ instead of 12.3966942€. The rounding cannot be disabled due to restrictions of brick/math.

3. The final calculation is:

   • € 12.40 * 12 = € 148.80.
   • Adding the VAT: € 148.80 * 1.21 = € 180.04800, which rounds up to € 180.05 instead of € 180.00.

This rounding leads to an incorrect total price.

Steps to reproduce:

1. Add a product priced at € 15.00 (including 21% VAT) to the cart.
2. Set the quantity to 12.
3. Observe the total price being calculated as € 180.05 due to the rounding in the cleanExclusive function.

Expected behavior: The rounding should be avoided in the cleanExclusive function or handled differently so the exclusive price is not rounded prematurely. The total should be € 180.00 instead of € 180.05.
The product price of € 15.00 (including 21% VAT) is divided by 1 + ($factor / 100) to get the price excluding VAT: € 12.3966942. Price excluding VAT multiplied by product quantity 12 = € 148.76033 + VAT = € 179.999999 which will be rounded to € 180 .