After the board of review has completed its review of the assessment roll, the assessor shall prepare a copy of the assessment roll, to be known as the “City Tax Roll”, and upon the certifications of the several amounts to be raised, as provided in Section 10, the assessor shall spread upon said roll the several ad valorem taxes according to and in proportion to the several valuations set forth in the assessment roll. To avoid fractions in computation on any tax roll, the assessor may add to the amounts as prescribed by statute. Any excess created thereby on any tax roll shall belong to the city.