If you really need to exchange at the airport currency exchange counters i suggest converting only enough for a day or two as the exchange rates are quite poor. There is quite a spread between the buy and sell rates from the then official exchange rate. I'd tip a dollar as suggested by a previous poster until I find an ATM machine.

You are likely better off using an ATM machine for currency conversions. Keep the receipts in case you need to convert back at the airport on departure. I always withdraw using my ATM card and my ATM card provider refunds any fees charged by the ATM's bank for the withdrawal and at the end of my visit the Rupees left over are enough for tipping on my next trip.