When you itemize you can choose to deduct either state income taxes
or state sales taxes, but you can't deduct
both. There is a standard amount for sales tax deductions based on your state, but you can deduct a higher amount if you have the actual receipts. The trick is that if the sales tax rate you paid for your car purchase is higher than the general sales tax rate, then you can only deduct the amount of sales tax that is attributable to the general sales tax rate.
California has high income tax and high sales tax. You'll have to crunch the numbers to see which results in the higher deduction. The
instructions to Form 1040, Schedule A have the details.