The cost of consumer items is up by 0.4% on May last year.
The figures released by the CSO show the biggest increase was in the cost of sending children to school, which has jumped by nearly 5% in the past year.
The cost of alcohol and cigarettes is up by 4.3% while clothing and footwear prices came down by 2.7%.
In comparison to prices in April, the cost of water, gas and other fuels all fell by just over half a per cent.