Sorry, I've never had really had the need for an easy dollars to shillings formula, on the rare occasions I need to convert them (like paying my South African satellite subscription) I just multiply the dollar amount by 85 using the calculator on my phone or laptop.
If I wanted to do it mentally I'd multiply the amount by a hundred then deduct 15% its pretty easy
73 x 100 ie add two zeroes = 7300 then take one of the zeroes off - 730 (10%) half it - 365 (5%) add together = approx 1,100 and then subtract from 7,300 = approx 6,200
But won't you be more interested in doing it the other way because you will see prices quoted in shillings so want to know the dollar price
Edited: 4:26 am, September 29, 2012