The two days prior to Christmas Day was up 10.4 per cent on last year for the same group of merchants.
Spending on the day after Boxing Day was down 23.6 per cent nationally, but the sharper decline was likely due to this day falling on a Sunday this year, Paymark said.
Most Paymark regions saw lower numbers for Boxing Day, the only day analysed by Paymark by region so far.
Auckland/Northland, Waikato, Whanganui, Palmerston North and Wairarapa saw slight jumps in Boxing Day spending.
A Paymark spokesperson said there could be any number of reasons as to why spending was down, from shoppers spending online instead, to even the weather.
Turley & Co property strategist and valuer Pat Turley said the Boxing Day sales "are at odds with Hawke's Bay's very good economic momentum and performance that is assisted by domestic tourists".
"Hawke's Bay is geared to homegrown visitors and tourism marketing has been very successful.
"Paymark figures represent one day that is a big shopping day online and the sales numbers exclude food and hospitality."