Anyone using New Zealand’s roads contributes towards their upkeep. Most road users pay levies when they buy fuel. Others, such as drivers of light diesel vehicles and heavy vehicles like trucks, pay through road user charges (RUC).
In New Zealand, all diesel vehicles required by law to pay road user charges (RUC). Vehicle and Fleet owners are subject to hefty fines if RUC are not kept up to date.
You can find more information in the official NZTA website
http://www.nzta.govt.nz/vehicles/licensing-rego/road-user-charges/
http://www.nzta.govt.nz/vehicles/licensing-rego/road-user-charges/ruc-distance-recorders/
For an Online Road User Charges (RUC) calculator
https://www.transport.govt.nz/land/road-user-charges-ruc-and-petrol-excise-duty-ped/online-ruc-calculator