Figures from electronic payment firm Paymark show $3.45 billion was spent across the country last month, down 0.8% on May 2008.
The total number of card transactions was up 6% overall, with usage of debit cards up by 7.8% and credit card usage up by 0.4%.
Food and liquor outlets are again among the fastest-growing sectors. Clothing and footwear retailers also experienced moderate growth for the month.
Spending at service stations was down 19%, largely because of lower fuel prices. Accommodation and travel outlets also reported shrinking spending.
