While out shopping for new clothes, Zen sees a sign for cozy socks advertised on sale for $3.50 per pair. The regular price of the socks is $5 per pair. Zen buys 5 pairs and notices that the socks do not ring up at the advertised sale price, so she has the cashier do a price check. If the sales tax is 9%, how much does Zen save by paying attention at the register?