Sales Tax calculation is incorrect

When you work through the sales tax entry in TurboTax, you will see on the Tax and Interest Deduction Worksheet where you will get a deduction for the sales tax on your vehicle and another deduction for the rest of the sales tax you paid during the year on other items, based on your income. So, the tax on the vehicle purchase is not being doubled:

Also, you may be confusing the car registration fees with the sales tax on your vehicle purchase. That is entered in a separate section under Cars and Other Things you Own. You enter the sales tax in the Estimates and Other Taxes paid section. I think you may have entered the sales tax in both sections by mistake.