AITA for asking for the exact amount of money I’m owed from my friend

When my friend owes me money he usually sends me the money he owes me. But recently he’s been sending me my money with about $5-$10 missing. I’ve been ignoring it the past couple times because I thought it was silly to argue over a couple dollars, and it really doesn’t make much of a difference anyway. But now that’s it’s becoming a little bit of a pattern I’m getting confused about why he’s doing this. Is it weird to ask him to just send me the exact amount he owes me? It seems dumb to ask for a couple dollars back, but it’s also a little weird that he’s leaving off a certain amount when he knows how much he owes me. And it’s usually in even amounts of money to pay back like $50, $80, etc. So, it feels a little weird to always leave off a couple bucks at the end. He also has made a few comments about how I make more than him so these things aren’t as big a deal to me, and that’s a little true but I don’t think that gives him the right to keep little amounts of money from me. I also don’t know how I’d even go about asking him for the money I’m owed because the amount is so little each time it just feels silly.