Hi there,
First of all thnx for youre answer.
I disabeled the tax totaly and it is stil going wrong.
The weird thing is that i have a regular product € 19,95 and the same product that can be designed with the help from a designer module € 19.95.
When i add the regular product to the cart is shows € 19.95. When i add the product from de designer module is shows € 20,-
I am begining to think that is has to do something with the designer module.