This is obviously a question of state law in your state, but normally a nonprofit, even if it is exempt from paying sales tax on the items it buys for its own use, has to collect sales tax on items it sells, just like any other vendor. Just because you are an “exempt” organization does not mean that you are exempt from collecting tax on items ordinarily subject to tax and remitting it to the state. To be sure, check with your state Department of Revenue.