Illinois Department of Revenue publication FY 2002-22 Changes for Form ST-556, Informational Bulletin To: All Businesses that Report Sales on Form ST-556, Sales Tax Transaction Return. New Illinois tax regulations have been adopted that affect Form ST-556. This bulletin describes revisions that we have made to Form ST-556 and instructions, and impacts that the regulations have on businesses that lease items then sell the previously leased items at retail. Many businesses that file Form ST-556 are affected by the regulations only because we have revised the form.