Too Mulch Math

I work at a home and garden center. We have a sale on mulch: five bags for $10. I wish I could say this happens only once but it actually happened several times a day:

Customer: “How much is black [Brand] mulch?”

Me: “It’s $2 a bag.”

Customer: “Oh, so it’s [Competitor] that’s running the five-for-$10 sale?”

Me: *Sighing* “Yes, sir. Us, too.”

Every single day.

I tried saying, “Five for $10,” but then I had to explain they didn’t have to buy five to get the sale price. I hated those sales.