You provided the easiest solution.
One 5 each from 5,10,15,20,30,35,40,45,55...70,80,85…
(excluded 25,50,75,100) so that's 15x1=15
Two 5s each from 25,50,100
Three 5s from 75
15+2x3+3x1=24
It was an easy problem. Why did I think its tough :/
Thanks for answering, everyone.