In addition to any other applicable exemption provided under this chapter, there shall be exempted from the measure of taxes imposed by this chapter all of the value or gross income derived by a fraternal benefit, religious, charitable, scientific, educational, or other nonprofit organization under section 501(c) of the Internal Revenue Code of 1986, as amended, from fees for convention, conference, or trade show exhibit or display spaces; provided that the gross proceeds of sales by a vendor through the use of exhibit or display space at a conference, convention, or trade show shall be subject to the imposition of the general excise tax under § 237-13.