Every employer carrying his own risk under the provisions of § 42-5-20 shall report under oath to the commission the employer’s actual cost incurred under the provisions of this title. The report must be made in the form prescribed by the commission by the fifteenth day of the third month following the close of the self-insurer’s fiscal year. The commission shall assess against the actual cost incurred a maintenance tax computed by taking two and one-half percent of the actual cost of operating under the provisions of this title as determined by the commission. The assessments must be paid to the commission which shall retain in every fiscal year the greater of fifty percent or two million two hundred thousand dollars of the maintenance tax revenues and use these funds to pay the salaries and expenses of the commission. The balance of the maintenance tax revenues must be remitted to the State Treasurer for the credit of the general fund of the State. In the event of failure to pay the tax within fifteen days of the date set forth in this section, the commission may assess against the self-insurer a penalty of five percent of the unpaid tax. If the self-insurer fails to pay the tax and penalty within fifteen days of notice by the commission, interest must be added to the amount of the deficiency at the rate of five percent for each month or fraction of a month from the date the tax was due originally until the date the deficiency is paid and the commission may initiate proceedings to withdraw the privilege of self-insuring in this State. The total maximum interest to be charged may not exceed twenty-five percent. The penalty under this section is payable to the commission. Fifty percent of the interest must be retained by the commission and used by it as retained maintenance tax revenues are used and the balance of the interest must be remitted to the State Treasurer for the credit of the general fund of the State.