The IRS has a formula that gives you a sales tax amount based on your income (the more your income, the more you are likely able to spend) and number of dependents (ditto). You can only add to that standard amount, additional sales tax for purchase of a vehicle, a home, or substantial renovations to a home.
If you try to use your actual expenses, and guess without proof and are audited, you will either lose the deduction entirely, or be switched over the standard amount (if the auditor is generous). Any tax deduction is a matter of legislative grace and the IRS does not have to award any deduction that you can't adequately prove.
Turbotax will automatically calculate the standard amount based on your income.
