Don't suggest other functions when I don't even understand the ROUND one
Fortunately, I am married to a maths teacher, and as he was looking over my shoulder as I was typing this, he promptly asked why I hadn't just asked him in the first place (answer: he wasn't around when the question was first raised) and he just now took me through the ROUND function. I will go back to my friend with a solution that I think should work.
Thanks for everyone's help