Exempt Class A vehicles have to be registered and licensed, but you don't have to pay the registration fee or the vehicle licence portion of the licensing fee.
You still have to pay for the other fees and levies included in the total licensing fee (eg the ACC levy and the fees for number plates and licence labels).
Exempt Class A vehicles are:
a pedestrian-controlled goods service vehicle
a motor vehicle propelled and supported solely by self-laying tracks
an all-terrain vehicle
any mobile machinery* used on roads only in road construction zones, in accordance with notices declaring those zones.