You have to tip frequently in Delhi but only small amounts like 20 or 10 rupees. But these bills seem to be hard to find, so whenever you get a chance, get hold of these bills because you will need them.
There's an excellent video which talks about a few other travel tips in Delhi: www.geobeats.com/videoclips/india/new-delhi/traveling-tips
When visiting a city like Delhi, I found travel preparation even more important than usual.
All around Delhi