You could create a calculated field (or an auto-enter calculations field, if your data allows for that) that you would use for display purposes.
For example, if your field was named, "Number," "DisplayValue" could be equal to the following:
Number & If ( Right ( Number ; 1 ) = ")" ; " " ; "" )
This adds a space to the end of each value if there is not a right parenthesis there. (Substitute whatever closing bracketing character you're using for negative numbers.)