Sales tax for vehicle sales should be calculated on where the vehicle is registered, not where you bought it. You got lucky where the dealership didn’t notice this mistake. I live in Allegheny County and purchased a vehicle from a dealership in Westmoreland County and they charged me a 7% sales tax after initially including 6% in the final worksheet because they noted that the vehicle would be registered in Allegheny County. My guess is that if you do go far enough away to somewhere like Blair County where they don’t deal routinely with that situation it would probably get overlooked.