In TN and a few other states, when you go to register a vehicle less than a year old and the purchase was out of state, the county tax assessor will collect sales tax unless you have documentation proving sales tax was paid where you purchased it. Both fivers we've bought, we bought from a dealer in MS. They collected sales tax and I had to sign a form for MS saying the sales tax did not belong to them, but to TN. Then when I went to register the fiver, I had to show the contract that detailed me paying TN sales tax. I was smart on the second one, the first one, I had to go back home to get the contract or pay an additional $2000+ in sales tax for a $14 license plate (ya, TN is greedy 9.25%).
There are sort-a-kind-a ways around it, but they are sort-a-kind-a illegal, and not worth it if your caught.
Larry