No tax shall be imposed as provided in § 58.1-1736 if the vehicle is:
1. Rented by the United States government or any governmental agency thereof;
2. Rented by the Commonwealth of Virginia or any political subdivision thereof;
3. A self-contained mobile computerized axial tomography scanner rented by a nonprofit hospital or a cooperative hospital service organization as described in § 501(e) of the Internal Revenue Code;
4. A self-contained mobile unit designed exclusively for human diagnostic or therapeutic service, rented to a nonprofit hospital or a cooperative hospital service organization as described in § 501(e) of the Internal Revenue Code, or a nonprofit corporation as defined in § 501(c)(3) of the Internal Revenue Code, established for research in, diagnosis of, or therapy for human ailments; or
5. A truck, tractor truck, trailer, or semitrailer, as severally defined in § 46.2-100, except trailers and semitrailers not designed or used to carry property and vehicles registered under § 46.2-700, with a gross vehicle weight rating or gross combination weight rating of 26,001 pounds or more, in which case no tax shall be imposed pursuant to subdivision A 1 of § 58.1-1736.