Generally speaking, when you are adding up your business expenses, you use all of them. If you are self-employed, the entire amount that you spent is deducted on Schedule C, assuming you weren't reimbursed separately and the reimbursement wasn't included in your income. Don't back out sales tax.
If you are an employee, if your employer had a reimbursement policy, and the reimbursement was NOT included on your W-2 because you had to account to your employer for your expenses, then you would enter all of your expenses in Employee Business expenses, then deduct your reimbursement so that you only claim the unreimbursed portion of your expenses.
If you are an employee, and your employer either didn't reimburse you or included your reimbursement in your W-2, then you would deduct all of your expenses.