Required rounding rules for AFR interest on loans (opens in new tab)

In the US, pursuant to section 1274 of the Internal Revenue Code, certain loans must charge interest rates equal to (or greater than?) the Applicable Federal Rates (AFRs) published periodically by the IRS or else face tax consequences. However, I cannot find out exactly what rounding rules are supposed to be used when calculating interest for such loans. Specifically: Is interest rounded to whole cents, whole dollars, or something else? What rounding method is used? Is it "round to the neares...