If you collected sales taxes, include the taxes in your income. Then, you deduct the sales taxes (which you sent to the state) on line 23 of Schedule C.
In TurboTax Self-Employed, go to Business->Business Income and Expenses->Business Expenses->Other Common Business Expenses. You enter this in the business expenses section under Taxes and Licenses. This will populate line 23 (Taxes and Licenses) on Schedule C.
See also this article from TurboTax on sales taxes for online sellers.
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