Let's say the sale price of the goods sold was $100,000 and you collected $7,000 in sales tax, so your total receipts were $107,000. You turn over the $7,000 to the state that same tax year. Let's say our cost of goods sold was $70,000 and, for simplicity, you had no other expenses. Your return would show $107,000 of receipts less 70,000 cost of goods sold and less $7,000 for sales taxes paid. Your net income on which you'd pay tax is therefore 107,000 - $77,000 = $30,000.
Now let's say there were no sales tax in your state and you simply sold the $100,000 worth of goods and had the same $70,000 cost of goods sold. Your net income on which you pay tax is now $100,000-$70,000=$30,000.
So, you see, it comes out the same either way. You do not lose out by including the sales tax and then deducting it. As I said, it's a wash so long as you paid over all the sales tax you collected in the same tax year that you collected it.