What if I pay with a $100 bill at a retail store, but the cashier doesn't have enough change? Will I just lose the money?

Sometimes when I go grocery shopping, I'll have a $100 bill and the grocery items will be like $30 so I give them the $100 so I can get $70 in change. But what if the cashier doesn't have $70 to give me, do I just lose that money?