How hard is it to have $20 in ones on you every week. You know it is coming.

Have her pay you by check.

Try that at the grocery store

The only time I'd be annoyed even a little is if they overpaid me like $8-10 one time, I ask is they need change, they say no keep it and then they deduct it the next time without telling me that's their plan. Even then it's not that big a deal. Start carrying change op.