In collecting taxes on unsecured property the tax rate to be used is the rate for property of the same kind on the secured roll last fixed before the lien date for the taxes to be collected. In the event that the assessment ratio is changed, the tax rate for unsecured property shall reflect the difference in ratios and shall be based on the assessment ratio for the current year. In collecting taxes on unsecured property that escaped taxation in any prior year or years the rate to be used shall be the rate to which the property would have been subject if it appeared upon the roll in the year when it should have been lawfully assessed. In the event the assessment ratio is changed, the assessed value utilized in determining the amount of the escape assessment shall be that which would have been employed in the year when it should have been lawfully assessed. The taxes on unsecured property shall be computed in dollars and cents, rejecting the fractions of a cent.