I had the same problem and wrote this.
=IF(I848>0.75,(TRUNC((I848-0.005)*4,0)+1)/4,MAX((TRUNC((I848-0.005)*8,0)+1)/8,0.5))
Here I848 was the calcualted cell. What I wanted to accomplish was base plates smaller than 0.75 round to the nearest 0.125 such as 0.5, 0.625 or 0.75, but never less...