Yeah, in my experience this is standard billing practices of many dealerships.
Before I had words with my dealership and they flagged my account for when I come in now LOL, I noticed that in fluid changes they would skimp. So if your engine needed 5 quarts of oil, they would put in 4 or 4.5. Over the course of a day that can add up to a large savings that the techs all share in.
It burned me to end when I checked my fluid levels after a change and went in and complained and told them I would never go back. They gave me a $220 service credit and said this would never happen to me again.
I have since become friends with the check-in person and he explained it all to me how it works and showed me my account that says VIP which he said means they know not to skimp out or cheat out of anything LOL.
They used to not be that way, and in the past, the issue I always had was they overfilled it and spilled oil all over the engine so it would burn off on the way home. He said they went to a bonus structure and saw a tremendous reduction in wasted materials, etc. that they said helped made sure they didn't spill oil all over the engine refilling it, but as anything, once money got tied to it and the techs had an incentive to not be wasteful or take their time, some take it to the extreme.
And yes it rubs me the wrong way too. They should just lump sum it and say it is $XXX dollars and be done with it.