I was beaten to the punch on bring this up but it's important. What no one seems to remember when they talk about the "internet sales tax" is that unless the federal government decides to put their own tax on internet goods this isn't a new tax. The problem is that they don't collect the tax, you are still required to pay it when you are a state citizen using it there (or some legal ruling of the sort) generally in the form of the use tax. Some states I believe still count it as the sales tax and just say that you have to self report/pay it yourself, the end result is the same though it the same % and you are supposed to pay it regardless. The problem? No one does. The general argument from internet companies is that they shouldn't be required to shoulder the expense of collecting and paying ever state their share, this has generally been accepted as a legitimate argument in the end but always gets brought up again because the honest fact is that it IS a tax on the books that never actually gets collected (and always gets extra looks around budget time for that reason).
It isn't interstate taxation and has been upheld as that multiple times. The reason is simple: It only applies to you when you bring it in and only applies once. This is why you are asked if you have paid tax to other states before. If you pay the sales tax of another state you are not supposed to have to pay the use tax for it when you bring it into your state. If your state has higher tax you are supposed to pay the difference. The problem with internet sales is that for most states you don't pay it at all. I'm not going to lie, I haven't paid use tax but the fact remains that you ARE supposed to. Some cases of it are easier for them to catch. I know many states hit you if you can't prove you paid tax on your out of state purchased automobile for example (when you register it).
