FYI:

It is a use tax, not a sales tax.

So the tax is based on where the car will be used (ie registered) and not where it is sold.

Everyone is basically saying the same thing, but just wanted to clarify the nomenclature.

Also, if you buy from a dealer in a higher tax state, they MAY take the full tax for THAT state, and not your home tax rate. Your home state can file to get the tax due them from the state in which the car was sold... confusing? Yes. But sometimes worth it. Really when you are doing a transaction there are only two states involved and it is easier to figure out and discuss.