Re: Yo! Yank ... Er ....
The only way you can accurately determine the proper tax jurisdiction is by geolocation using the street address. This assumes the address used is the location of the buyer. Another wrinkle is if one buys something online while away from home, what is the taxing jurisdiction and how is it determined? Depending on how it is done, a VPN service might cause all sorts of fun (honest I was in Finland when placed the order).
The address to which the product is shipped determines the taxes. If you're a hundred feet the wrong side of a tax boundary and you've got a friendly neighbour the other side, see if they'll accept delivery of your packages.
This is where the UK VAT (admittedly with a simpler system) and South Dakota have it right - if you're under a financial limit then you don't have to pay but you can't reclaim anything either. Otherwise a retailer is going to require you to have a shipping address in their state so they can ship to that, and then it's your problem moving it from there to your home state.
Another option would be for the retailer to state at time of sale that the buyer is responsible for paying the sales tax direct to their state and that details of the transaction amount would be forwarded to the state to assist them in recovering it. That way, a small retailer could send a data dump every month or quarter to each state with all the transactions and then the state could ask people for their money. I think the California income tax forms already have a section where you can declare stuff where you should pay tax but haven't.