The average spend per customer was up, Mr Cossar said, rather than the number of visitors.
The Lions tour brought a large number of British and Irish visitors to Rotorua for the local match.
"We are seeing good visitation occurring even outside of the Rotorua Lions versus Maori All Blacks game.
"We've also had an influx of key media from the British market - ranging from the BBC to the Daily Telegraph and the Daily Mail among many more which results in valuable international profile for our business."
Tourists spent $48m in Rotorua in May, and $55m in the remainder of the Bay of Plenty region.
Destination Rotorua chief executive Michelle Templer said marketing of Rotorua was focused on encouraging visitors to "stay longer and do more".
"It is fantastic visitor spending continues to increase in Rotorua."
Nationally, spending rose by 8 per cent in May, and 6 per cent over the year.
This was helped by large rises in areas such as Northland, Lake Wanaka, Fiordland and the West Coast.
Year on year growth was less significant in the main centres - 1 per cent in Wellington, 2 per cent in Christchurch and 4 per cent in Auckland.
MBIE's Mark Gordon said the figures were useful for tourism industry planning.
"Tourism spend information for the regions helps inform investment and planning, providing insight into where both domestic and international tourists are spending their money."
Among international visitors, those coming from China spent the most money.
Australians spent more overall than Chinese visitors in the wider Bay of Plenty region.
The highest amount of money was spent on retail, followed by food and beverages, then culture, recreation and gambling.
The amount spent on cultural activities, recreation and gambling was particularly high in Rotorua - $7m compared with $1m in the rest of the Bay of Plenty.
