Originally Posted by MadDog
Which is why CA doesn't call it a 'sales tax' when you register a car from out-of-state. They call it 'use tax', which just happens to be at the same rate as sales tax.
But, if you've owned the car for more than a year, you don't pay the use tax.
All states who have sales taxes also have what is known as use tax which is applied to anything which you do not buy in that state or from a company who has a business entity in the state. If your state has a sales tax, then anything and everything you buy over the internet you are required by state law to pay the use tax on those items. No one does and this is what got many states pissed off and why they been trying to lobby for a federal sales tax that all online retailers would have to collect and pay to your home state.
Anyway, to the op, whether you pay a sales tax or use tax on a car, could depend on a number of things. Some states will make you pay it if the car has been bought in the last 6 months, they assume you bought it elsewhere to avoid the tax, unless like it was pointed out you can show you paid a sales tax in another location. However, if you owned the car for a period of time you can pretty much can go into any state and register without having to pay any sales tax. This does not mean you will not have to pay a registration tax like VA and CA have.
As Freakazoid pointed out, you could register the car in PA if it older than 6 month and you were not a prior resident and not pay the sales tax, and the registration fee is only $36 a year and that is all you pay in PA. As with PA many states will look at where you were a resident when the car was purchase to determine if any sales or use tax is paid.