The course ordering calculates wrong VAT value.

Reproduce:
1. set up a course with the final prize 1190
2. set up a course ordering with VAT 19%

Expected:
Cost without VAT: 1000
VAT: 190

Actually happens:
Cost without VAT: 963,90
VAT: 226,10

Here, 19% is calculated from the final prize 1190, but must be calculated from 1000