I was tipped off that the Rio (a Caesars property) has some full pay machines at lower denominations including 8/5 Bonus and 9/6 Double Double Bonus and these give 1 tier credit for each $10 coin in -- not the $25 per tier credit at other Caesars properties in Vegas.

But be careful, some Bonus games are 7/5 so you have to check the paytables before your play.