@Bas: Hey I checked it out ... I really like the shopping cart, and how I can see everything I've added really easily. The running total animation is nice. I kept hitting right-click, expecting something ... I think you should add something there, anything that makes sense (even a link to "Home") would be good, so that there's some response. Also, I find it hard to read Dutch.
I will have to try it out on the Surface later; I've only had the chance to try on the desktop without touch.
I hope you get a lot of suggestions and the app makes you enough money that you don't have to work on stuff you hate.