You are posting your question from the Free Edition, which does not support entering any itemized deductions. Are you actually using a higher version of the software and planning to enter other itemized deductions such as mortgage interest and medical expenses or charity donations, too? If not, then entering sales tax will have no effect at all on your tax refund or tax due. Sales tax is an itemized deduction which has no effect unless you have enough itemized deductions to exceed your standard deduction.