Normally, sales tax is not paid when purchasing real estate. You would want to verify that you actually paid sales tax before entering an amount.
Per the IRS Instructions for Schedule A (1040) Itemized Deductions, page A-6:
State and Local General Sales Tax Deduction Worksheet Instructions:
Line 7. Enter on line 7 any state and local general sales taxes paid on the following specified items. If you are completing more than one worksheet, include the total for line 7 on only one of the worksheets.
If you elect to deduct state and local general sales taxes instead of state and local income taxes as an itemized deduction on Schedule A (Form 1040) (you cannot deduct both):
To figure your state and local general sales tax deduction, you can use either your actual expenses or the state sales tax tables. TaxAct will use the higher of state and local income taxes, or state and local general sales taxes to report on Line 5 of Schedule A.