Machinery and tools, including repair and replacement parts, used directly in cleaning motor vehicles by a motor vehicle cleaning business shall constitute a classification for local taxation separate from other classifications of machinery and tools as defined in § 58.1-3507. The governing body of any county, city, or town may levy a tax on such classification of property at a different rate from the tax levied on other machinery and tools. The rate of tax and the rate of assessment shall not exceed that applicable to the general class of machinery and tools.