sales tax on our web stores

Is there a sales tax feature available within any of our extensions or pre-builts?
Legally, we are responsible for collecting the sales tax of any buyer (in the US) depending upon the state in which they are buying. Then, we have to pay it to how many agencies? 50!?

This is very problematic.
Do we pay it periodically?
What happens if we pay it and then have to uncharge a card for a returned product?
How do you get money back from the State? Good luck!!
Must we create separate bank accounts for each state,? What happens to the interest made on each state's tax account?
Do I have to pay taxes on it?
Taxes on taxes... hmmm.
Anyone got some experience, documents, software, extension, ideas?

best wishes,
chris