This is denied by the police however. Superintendent Stephen Greally said there had been no change in the police approach to cycle safety.
He said safety on the road was a priority for police, whether the road user was in a car, on a bike, or using some other form of transport.
"There has been no change in the way police enforce laws for bicycle related offences," he said.
"When an officer attends a job, they are responsible for assessing the situation and providing an appropriate response to ensure the safety of the public.
"The response from an officer could range from an infringement notice to a warning or prevention advice, this decision is made at the officer's discretion."
Mrs Casey also said the shop has sold a lot more bikes lately, and estimated 95 per cent of cyclists wore helmets.
Cycling Action Network's Patrick Morgan also thought the fall in helmet infringements might reflect changing police priorities.
"I think it's just police have better things to do than stop people on bikes and fine them for helmet use or misuse," Mr Morgan said.
"I welcome police resources going into higher priorities."
Mr Morgan says there was "thin" evidence mandatory helmet use laws worked, and Australia and New Zealand were the only two countries to have such a law.
"There's enough evidence that mandatory bicycle helmets hasn't worked as intended, and that's why it's our policy to review the law, to see if it's working as intended - but it's not our top priority."
He said CAN's position was not a call for making helmets optional, but to review the wider effects of helmet-wearing legislation.
Mr Morgan said he did not normally wear a helmet when cycling on the road.
He has a legal exemption - on medical grounds because helmets gave him headaches and migraines. He said he was stopped three or four times a year.
"I wear it if I do something dangerous, like mountain biking or something risky like that. But [not if I'm] just riding around my neighbourhood or on a separate New Zealand cycle trail."
Mrs Casey said the helmet law was accepted in Rotorua, but there would always be hardliners who refused.
"You're always going to get people that won't, that's the biggest issue ... and they never will, and they'll never pay the fine if they get one."