I thought your "real-world constraint" existed too. Then I had to keep track of thousandths of a cent.
When you have experienced the "no, a cent is no longer granular enough" problem, the conversion of DECIMAL(7,2) to DECIMAL(9,4) and the attendant code compatibility is something you'll appreciate.
When you have experienced the "no, a cent is no longer granular enough" problem, the conversion of DECIMAL(7,2) to DECIMAL(9,4) and the attendant code compatibility is something you'll appreciate.