I understand your legislative argument, but here, in Quebec Canada, this is how we work. We HAVE to use the right calculation to obtain the right result. We have a way to calculate the taxes and every shop is calculating it that way : sum up everything and apply the taxes. It's not that complicated. But VirtueMart does not offer this kind of solution right now. That's why i'm trying to explain everything.
Here is a really easy exemple, step by step, with random prices. This is how we work here :
product 1 price : 5,50$
product 2 price : 14,25$
Shipping price : 5,50$
Subtotal : 25,25$
Tax 1 (5,00%) : 1,26$ (25,25 * 0,05 = 1,2625 -> round that number)
Tax 2 (9,975%) : 2,52$ (25,25 * 0,09975 = 2,5186875 -> round that number)
Total : 29,03$ (Subtotal + rounded taxes)
See? That simple. The taxes are calculated and rounded once on the subtotal only.
Actually, in virtuemart, the taxes are calculated on the products price, and then on the shipping price, and finally added together. It's not gonna give the same result. The way VirtueMart is calculating it is not an error, but that's not the way we need to calculate it here. This is why I ask for an option to calculate it the way we need.