I'm pretty exacting when it comes to amounts, bills, and totals. A lot of my friends aren't. When we go to a restaurant, I always order water and there are various other reasons my bill's significantly lower than theirs. So when the time comes and I have the waitress print out separate checks. Most people are like "Oh, we could have just split it down the middle!" No, I'm not paying three or four extra dollars every time I go out with you. Or when I owe someone something like $1.75 because they bought me coffee and they're like "I hate change. Can you just give me $2?" Usually something like "If you hate change so much I can just give you $1" shuts them up. Is it nickel-and-dimeing people to death? Maybe. But now I have a jar with about $75 worth of nickels and dimes at home.
I will calculate things pretty precisely--so a credit card tip might be for $5.45 rather than a round number of dollars--but there are also people with whom I then average the bill, on the theory that it will even out over time. (This includes someone with whom I have been doing this since the 1980s.) But I agree that if someone says they "hate change," it's for them to round in my favor, not the other way around. I was, however, amused recently to see a post from someone who was told his bill was 2.55, and said 2.56 would have been cooler. The shopkeeper let him pay the extra penny, and everyone was happy. Silly, but silliness in the direction of "let me give you a tiny bit extra, because I like certain numbers," not an attempt to get a discount.
There's a rather-akin thing, which occasionally causes a bit of disharmony between my brother and me (most of the time, we get on very well together). He's borderline-innumerate, as he would be the first person to admit; one function of this, is that he utterly loathes any precise fussing-over, and analysis of, amounts of cash owed to him (or by him) for shared purchases / meals / whatever: he can actually get very angry when a companion "subjects him to" such stuff. At the same time, he definitely wants the other person to contribute their fair share. I accept that it's a genuine quirk of his, not a ploy to try to get the other bod to shell out more than their proper share; and when he calms down after such an anger episode, he's apologetic. I do find it annoying, though, to have to rather walk on eggshells around him over this particular thing; and to have to plot and plan ways of rightly reimbursing him, which won't throw him into a rage.