my parrents always make me do this in restaurants and I have found a hack for multiples of 5 % so
15%=10%+5% so find 10% then half it, then add it to 10% so
10% of something=10/100=1/10
5%+5/100=1/2 of 1/10 so find 1/10 of 35
1/10 of 35=35/10=3.5
half of 3.50=1.75
add that to 10%
3.50+1.75=5.25
tip=5.25
tip+bill=total
5.25+35.00=40.25
total bill=$40.25
