Tipping is not as widely practiced in New Zealand as in the United States or Europe, but in city restaurants and hotels it's appreciated if you acknowledge good service with a 10% tip. Tour guides and drivers would also be used to receiving some gesture, even though it isn’t mandatory.
Taxi drivers will appreciate rounding up the fare to the nearest NZ$5 amount, but don't feel you have to do this. Porters will be happy with a NZ$1 or NZ$2 coin. Most other people, like bartenders, theater attendants, gas-station attendants, or barbers, will probably wonder what you are doing if you try to give them a tip. The nice thing about this is good service in New Zealand is given because the person means it, not because they’re aiming for a good tip.