I have a calculated number that I want to display to the ½ fraction. The
fraction format rounds up.
Even if I use the rounddown to get the number I want, when I format the cell
to the half fraction, it rounds my number back up again. Ive tried
increasing the decimal places of the original calculated number and that
doesnt help.

Im trying to calculate paid days earned (based on hours worked).

Even if you work enough hours to get 1.49999999999999 days, you dont get 1
½ days until you cross the 1.5 boundary.