Revenue has received more than €60,000 in 'conscience money' in the last three years.
They stress they do not encourage that approach and want people to pay the correct amount of tax.
The Sunday Times reports a single bank draft for more than €30,000 was sent to a revenue office in Limerick in 2016.
It is thought the anonymous payments could have been made by people who may have evaded tax over time and wish to make restitution.