In billwerk, invoice items are rounded to two decimal positions. The rule "round half up" is appled. This rule is also known as mercantillist rule.
The total amount of an invoice is calculated from the rounded invoice items.
The only exception to rounding per invoice item are discounts where the reduced amount is displayed in a separate invoice item. This can be controlled using the option "Create separate invoice item for the discount" in the settings of the discount.
In this case, the price is first calculated and rounded after discount assignment. The amount of the discount item is then derived on the basis of this amount. An example:
Product A, price = 9,99 €
Discount on product A = 50,00 %.
Amount to be paid = 9,99 € * 0,50 = 4,995 € = 5,00 €
4,995 € are rounded up to 5,00 € according to the round half to even rule.
A discount without an additional invoice item results in the following final result: