Agree with this - Having both figures on a single item would look messy.
But I agree with the other sentiments that showing the rounded figure would make it harder to find things and match them up.
The perfect solution for me, would be to show the actual figure, with a little pig in the corner.
If I’ve spent £9.45, I know that £0.55 has been moved to coin jar (or whatever pot it is), I don’t need to be told that.
However… Kudos to Monzo for listening in the first place (tidying up coin jar), I’m sure they’ll work something out.