You can deduct the sale tax (but not the registration) paid on a car purchase as a major purchase in the sales tax section. It is an itemized deduction. You may get a tax benefit if the total of all your itemized deductions is more than the standard deduction.
To enter it, click on the Search tab then type sales taxes paid in the search box and click on jump to. Select the Easy Guide when you come to that screen and enter all the detailed information about where you lived and total sales tax rate and you will come to a screen asking about major purchases.