This app was mentioned in 5 comments, with an average of 5.80 upvotes
Check out the Gaspy app which informs you where the cheapest petrol is at the moment based on your location in New Zealand.
Currently the Caltex on Hutt Road (along Kaiwharawhara Gorge) is coming up as the cheapest in the Wellington area.
Gaspy https://play.google.com/store/apps/details?id=nz.hwem.gaspy&hl=en_NZ&gl=US
And if you're in Auckland, fill up at Gull Portage Road
This app is a good way to force more competition in the market: Gaspy
https://play.google.com/store/apps/details?id=nz.hwem.gaspy be a smart kiwi and use the AI that is available.