NZPost is now charging rural delivery fees on all packages instead of just the tracked ones. Due to this there is now a $4 rural delivery fee on on Rural orders. If your address is rural and you do not select it as such when checking out, you will receive a $10 invoice to cover the rural delivery fee and the new invoicing costs.
If you are not sure if your address is rural you can check it here. For futher information regarding the increase please read about it at NZPost here