Increase / decrease font size dependant upon number of decimal places

I have a spreadsheet where I record the length of time a member of staff has worked. Staff can work between 0.25 hours and 12.5 hours. I have worked out how to show decimal places only if there are any i.e. 12.00 would return 12, 11.50 would return 11.5 and 10.75 would return 10.75 etc. What I want to do is decrease the font size from 12 to, say 11 point, if the value of the cell has one decimal point and 10 point if the value of the cell has two decimal points. Any ideas