if I purchase a car from another state where do I pay sales tax?

Probably where you register it , If you bought it in New York and live on the moon they'll still want a piece of the action

You pay sales tax to your home State, as beatupchevy said, when you do the title transfer and initial registration. On a side note, if you're buying long distance and can't inspect the vehicle yourself, have it inspected by a professional inspection company before you decide to buy it! Never ever buy a vehicle, especially a used one, sight unseen!! I've used lemonsquad.com for my long distance purchases with excellent results! Jim