Every county, city or town convict in this state, whether required to work upon the public highways of the county, city or town, in accordance with the laws of this state, or merely confined in the county, city or town prison, shall receive credit upon his or her fine and costs of One Dollar ($1.00) for each day confined in prison, or worked upon the public highways, rock pile, or rock crusher, or public work; provided that those prisoners or convicts doing and performing the most efficient work and making the best prisoners, shall be entitled to an additional credit of one (1) day for every five (5) days of work, the custodian of the prison to determine at the end of each five (5) days of imprisonment whether or not the prisoner is entitled to such credit, and to make a record of the decision and notify the prisoner of the same.