The ‘road tax’ circulation tax is imposed by the town hall in the municipality in which the owner is resident.
It is normal that one must know that they must pay the tax, same as IBI, rubbish collected, garage entrance tax etc.
You will not be able to transfer the ownership until the tax has been paid (I believe that includes the year in which the sale takes place, e.g..1st Jan 2012, the tax for 2012)
On an occasion when I sold a motorcycle in around March, we had a problem as the tax due for that year was not known by the town hall.
ALSO Do not fail to ensure that the ownership has been transferred to your friend, otherwise you will be legally responsible for the vehicle, road tax, fines etc ’for ever.’