How to cut pills to taper

I see that I should maybe reduce by 5-10% a month. How do you accurately cut pills to get to proper reduction amounts? Say I’m at 75, and need to reduce by 7.5 (10%) to 67.5. I have 25 mg pills. So I can cut a 25 mg in half to 12.5 and add that to 50 and get the desired 67.5. That’s easy. But when I go to reduce from 67.5 by 10% to about 61, how can I do that with 25 mg pills accurately? Thanks.