Which field is better to keep Decimal position in Microsoft Dynamic GP2010

I have one requirement.

I need to show Quantity field with specific decimal positions. This decimal positions i have to give the option to user set in Microsoft Dynamic GP 2010. using that field i will get how many decimal user need. (this data i am going to save in table which is i created  in company database)

Let me know which field is suitable for get the decimal positions.