1) They're all different
2) 0
3) No
4) You need to maintain the table by going to every state's website (and many counties) regularly, and keeping the rates up to date.
That's why this is a specialty business. I've been doing accounting integration for over 20 years, and I wouldn't think of doing this myself, there are too many liabilities. Many states have special offices and workers whose full time job is to make sure taxes are correctly calculated, and you'll get fined if you don't do it right.
