An income tax is imposed annually at the rate of five percent on the South Carolina taxable income of an organization described in Internal Revenue Code Sections 501 through 528 (Exempt Organizations) and 1381 (Cooperatives) as computed under Internal Revenue Code Sections 501(b) (unrelated business income), 528(d) (taxable income of homeowners’ associations), and 1382 and 1383 (taxation of cooperatives). The modifications provided in Article 9 of this chapter and the allocation and apportionment provisions provided in Article 17 of this chapter apply for the taxes imposed by this section.