Re: 47 different state sales taxes
One of our clients decided to open a couple of US based shops, so one of our devs had a look a the local tax law to make sure we could process it correctly.
As far as anyone could tell from reading it, the tax law specified how fractions of a cent were to be rounded up or down, although from what we could tell, they just specified the standard if x<5 then round down, else round up.
We were all happier when their trial went bust, and we didn't have to expand to other states. At least European laws don't try to redefine maths.