The Commission shall, in the performance of its function and duty in assessing and levying the special regulatory revenue taxes provided for by this article, omit the assessment and levy of any portion of such taxes as are unnecessary within the Commission’s sole discretion for the accomplishment of the objects for which the regulatory revenue taxes are imposed including a reasonable margin in the nature of a reserve fund. The Tax Commissioner shall annually certify to the Commission the amount needed to sufficiently compensate that department for its estimated incremental costs to be incurred in the discharge of its statutory duties to assess and collect state and local taxes against railroad corporations. The persons and corporations upon whom such taxes are imposed are relieved from liability for the payment of such regulatory revenue taxes, except when, and to the extent that, the same have been assessed and levied by the Commission, in accordance with the provisions of this article.