what if I don't have a schedule a to input total sales tax rate. what is this needed for?

You posted your question from the Free Edition,which does not support entering itemized deductions.  If you are not entering itemized deductions like mortgage interest or medical expenses and charity donations, entering sales tax is useless to you.  

IRS Schedule A Itemized Deductions is used to reported itemized deductions rather than to claim the standard deduction on your IRS form 1040 income tax return.

To input 'total sales tax rate, in TurboTax Premium Online, select Deductions & Credits, then Estimates and Other Taxes Paid, then Sales Tax.