From the reams of comments on Africa tipping, I think the consensus is 10% of the daily rate. That's what I've always done, usually rounding up if the PH/guide works hard. I realize it's not Africa, but I think it's still a good guideline.
Have a great time in New Zealand.
...and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth. Gen. 1:28