It would help to see your actual calculation but you can try this out:
Int ( number ) & "." & Right ( "00" & Mod ( number ; 1 ) * 100 ; 2 )
It's also possible to set up data formatting to specfiy currency and two decimal places. You example might be set up as:
Johnny owes <<YourTable::YourCalcField>> to the library
You can then select the entire block of layout text and apply the data formatting to it. This assumes details about your database that may not be correct however.