For what it’s worth, without knowing more detail my guess would be this is a case of “Lemur can you lay these out for me… but oh by the way, I don’t like your values so can you make it half the size?” or something.
It could just be a different development style but I never hit this particular issue.
That being said, I’m on the other end of the scale where I find HTML nice for making pretty charts but abysmal for wiring up GUIs as hooking anything up to a model is generally very painful (or you are left with antiquated form processing that always reminds me of when http was hooked directly to shell scripts.)
I was a Swing developer since 1997 or so… so I automatically think in “GUI layouts”. I admit that Lemur may be tougher to layout if one comes at it top down versus bottom up.
Anyway, sorry to derail the conversation.
I will restate that the real issue you will have is tracking sales tax. This is why things like Steam are so popular because they will already calculate and collect the sales tax for you… or VAT tax in Europe, etc…
The choice of ‘how to collect the payment’ is only about 1% of the total problem. It’s the stupid-easy part.