Funny you posted this. I was noticing the same thing. My data source is a base sas table (no information map, just proc sql code) - I tried changing the formats within the sas table itself and then within the proc sql code. It actually was resetting EVERYTHING to BEST. format. So I even loose my $ signs.
Anyhow, you can run the following statement during your SAS ETL to round to the nearest .1 decimal place:
(you could change .1 to 0.01 to round to nearest one-hundredth ~ for instance)
I am pretty sure you could customize the expression in your information map to also do this. I'll test that idea next.
Actually with information maps, its really easy.
In the map, all you need to do is go to the properties of the data item, choose the 'Classification, Aggregation and Format' menu item, then select a format. When I choose dollar9. here, I actually saw my $ and no decimal places.