> 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.