Paymark says the unseasonally warm weather, coupled with more working days in July, appears to have encouraged shoppers to open their wallets a little wider.
Paymark, which processes about three quarters of all electronic transactions, says spending rose by 9.2% in July, compared to the previous July, with a total spend for the month of $4.04 billion.
Sales and marketing head Paul Whitson says warmer weather usually results in increased spending, but not all retailers are feeling so sunny.
"There are some retailers that are still doing it very tough out there, primarily in the high street, " he says. "We're talking about clothing stores, footwear shops and department stores. There is some growth but it's way below the national average."
On the other hand, Mr Whitson says, hardware stores are doing very well.
He says some of the lift is also due to a 10% rise last month in petrol prices, which make up about 1% of total spending.
On a regional basis, spending increased by more than 11% in Palmerston North, Marlborough and Canterbury.