Excise taxes are assessed annually on a calendar year basis by the Assessors of the town in which the vehicle is garaged as of January 1. If the motor vehicle is registered after January 31st, it is taxed for the period extending from the 1st day of the month in which it is registered to the end of the calendar year. For example, if a vehicle is registered on April 30, it will be taxable as of April 1, for the nine months of the year (April through December) and the excise due therefore, will be 9/12 of the full excise. In no event shall the excise be assessed for less than $5 nor shall an abatement or refund reduce an excise to less than $5.