> but wouldn't you need 101 sides to get 0% and 100% for that?
There is no 0% in d100/d-percentile rolls. Every "how to interpret these dice" paragraph in games which use them will tell you to interpret 0-0 on 2d10 as 100, not 0. Or, hypothetically (but i don't recall having ever seen this), they'll have a stated range of 0 to 99 (inclusive). Either way, the numeric range spans precisely 100 digits.
There are games that use a d100 with 0-99 range, and games that read a d10 as 0-9 for that matter. First that comes to mind is Ambush! from 1983 that did both those things (https://boardgamegeek.com/boardgame/1608/ambush).
Love that game, but it is a bit distracting that probabilities feel one-off. Rolling 5 or lower to hit is 60%, not 50%. And when rolling 2d10 the result is 0-18, not 2-20.