Similarly, where an organization sells certain types of goods or services to a particular class of persons in pursuance of its exempt functions or primarily for the convenience of such persons within the meaning of section 513(a)(2) (as, for example, the sale of books by a college bookstore to students or the sale of pharmaceutical supplies by a hospital pharmacy to patients of the hospital), casual sales in the course of such activity which do not qualify as related to the exempt function involved or as described in section 513(a)(2) will not be treated as regular. On the other hand, where the nonqualifyingsales are not merely casual, but are systematically and consistently promoted and carried on by the organization, they meet the section 512 requirement of regularity.