Store owner Andrew Spence said he and his team were "buzzing" when they found out.
"It was actually the team that let me know," he said.
"We'd had a remarkably busy week and I was enjoying a bit of a Sunday morning lie in when my phone went berserk about 8am and everyone was saying we'd sold a winner."
The Maadi Rd store has a history of providing winning tickets, with a punter claiming $12m in a Lotto Powerball jackpot in June 2005 – the second-highest win at that stage.
Three years later, a Big Wednesday winner took home $4.8m after purchasing their ticket from Andrew Spence Pharmacy.
Spence said he and his designer redesigned the store's Lotto winner's advert after he had "a feeling" a few weeks back.
"I just thought with the volume of tickets we've been selling, there is a better than even chance we may sell something significant," he said. "And that foresight paid off.
"We had queues out the door and round the corner in the week. It was a real buzz for all of us to be a part of the excitement of a Must Be Won draw."
This was only the seventh time Powerball has reached a Must Be Won draw with a jackpot of more than $30 million.
Lotto NZ Head of Communication and Corporate Social Responsibility Marie Winfield said she was thrilled the jackpot rolled down to allow 10 families to experience a life-changing win.
"Kiwis all over the country have been dreaming about what they would do if they won Powerball and now 10 lucky players are about to find out," she said.
Saturday's win follows two other Napier wins last weekend, which saw two of the city's residents take home $142,857 in Lotto's First Division.
Those tickets were sold at Tamatea Pak'nSave and Paper Plus Taradale.
A fellow Napier resident also won big in Wednesday night's draw, taking home $1m.
That ticket was sold at Napier City Pak'nSave.
A further 10 Lotto players will also be celebrating after winning a $100,000 share of Lotto First Division in Saturday's draw.
Four of the tickets were sold in Auckland, with one ticket each sold in Taupo, Tauranga, Carterton, Nelson, Wyndham and Canterbury.
Strike Four was also won by two players from Kerikeri and Auckland, who each took home $300,000.