first you have to make a counter that can go upto 0-100,because 7490 is only 4bit, then taking the out and give to input of another counter that is having a set function, from clock you have to use another out put to give you a pulse after every 5 counts, so this will act as the set pulse of the second counter. so the incerement of teh second counter will only occur every 5th clock and will show an increment by 5 each time, if you dont get what i say, can post a diagram later