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'. Upon receiving the certification of the several amounts to be raised, as provided in Section 10.12, the assessor shall spread upon said tax roll the several amounts determined by the council to be charged, assessed, or reassessed against persons or property. He shall also spread thereon the amounts of the general ad valorem city tax, county tax, and school tax, according to and in proportion to the several valuations set forth in said assessment roll. To avoid fractions in computation of any tax roll, the assessor may add to the amount of the several taxes to be raised not more than the amount prescribed by law. Any excess created thereby on any tax roll shall belong to the city.