What shape is a d100?
The d100 from the standard 7-dice set is a pair of 10-sided dice (in the standard pentagonal trapezohedral shape), one of which is numbered with the integers from 1 to 10 and the other of which has faces numbered in multiples of 10 (00, 10, 20, 30 and so on to 90).
How do you roll a d3?
A d3 is just a d6 divided by two, rounded up. A d3 is rolled by rolling d6, halving the result, rounding up. There’s no physical d3 for there to be rolled. The point of the character sheet roller is to emulate physical dice rolling.
Is a d100 fair?
They are not fair, they cannot be made fair, and they do not produce the same probabilities as rolling 2d10. A d10 is a pentagonal trapezohedron, which is a symmetrical fair die. Even an imperfect d10 is far more fair than a d100 can be, due to the limits of design.