Is car sales tax based on where I live or where I buy the car?

Generally, sales tax on a vehicle is based on where you will register it, which is usually where you live, not where the dealership sits. If you buy in another state, the dealer may collect your home state's tax, or you may pay it directly when you register at home. Some states give credit for tax already paid elsewhere. Rules differ, so confirm with your state DMV before buying out of state to avoid paying twice or getting a surprise bill at registration.