This is not possible on the Prizes tab. On the Prizes tab, prizes will be displayed with their actual, full amount. If however you wish to round the prizes in the Game window which is displayed to your players, that can be done. You'll need to make a small change to the layout. On the Layout tab, double-click the "Prizes" cell. The "Contents" section should have a value like this:
<prizes orient="horizontal">
Just change it to:
<prizes orient="horizontal" roundOff="true">
After you make that change, click the link below the Contents that says "Copy contents to all property sets". This will make sure the change is made for both odd and even rounds.