I was by and large homeschooled and self taught, but I also know I had excellent (and very exacting) teachers. I don't know as much of Muggle schooling, though I know some. I think it just depends on the school and the area and the system, honestly.
Though calculators really are helpful for change making. Work a shift and have a hard day, I think most people would have trouble at some point making exact change -- I know I would garble it when tired, and sometimes just when scatter brained, but I've never claimed maths as my high point, either. I don't brew my own stuff generally for a reason as well -- though for some reason I'm not a poor cook?