Showing my age, and I guess my privilege, but I don’t split expenses that way. (And on reflection, showing my trauma, too.)
As a principle, I try to keep my friendships generous and non-transactional.

If I owe someone and it’s not formal, I round up to the nearest whole amount and give or send them the money (besides, if a friend is counting out the change, they can keep my pennies). I usually tell friends they can cover me the next time — with no expectation that will occur. If a friend is adamant about giving me money, I’ll round down, usually to the nearest 5 or 10.

It would make me feel sort of weird to be given exact change from a friend. I think if a friend insisted on paying exact amounts, and then got it wrong in a way that underpaid me, I’d probably mentally flag it.
I suffered from a lot of manipulation and guilt around money when I was younger. It’s not that I’m super chill about money. I still notice the details, I just make a choice not to give value to money in the context of my relationships. (And forgetting ‘normal’ interactions is easy, because ADHD, so they just disappear into the void. Abnormal ones do get remembered.)
So the pattern would quickly stand out and the relationship would be handled appropriately. I’m not going to be party to micro-aggressions by a wannabe sociopath.

Mind you, this is either fake or that person is extremely dumb. I don’t think an actual sociopath would brag about it on social media - those sort of low-stakes ego games seem like something they’d keep in the dark. I just like exploring my feelings and positions in the form of long-winded comments that I sometimes actually post.