Varying number of decimal places for a field using Formula Editor

Hi

I have a field that displays a product price that I would like to conditionally format the number of decimal places that are displayed depending on another field value (in this case Unit of Measure) - eg no decimal places if being sold in Kgs or 2 decimal places in Metres etc

I have tried Format Editor, Number tab then Custom Style, Number tab & opening the Formula Editor for the Decimals value but cannot work out what formula I should be using.

Can anyone point me in the right direction please?

Thanks

Jon