Income tax is imposed on your profit, which is after all expenses. So if you had no other expenses, it would be on $100.
However, in many (most?) States Sales Tax is imposed on the BUYER, not the seller. The seller (you) merely forwards the sales tax to the State. In those cases, you are supposed to only report $100 as income, and $0 as an expense for the sales tax.
If you happen to live in a State that imposes the Sales Tax on the SELLER (you), then you should report $110 as income, and $10 as an expense.
