Rounding off of Amount fields in SAP

I remember, when I learnt COBOL, our instructor used to give us problems to solve. One of the problems often repeated in all programming classes was to write the code for rounding off numbers, without using built in functions. In SAP it is a bit tricky, as SAP stores amout fields as currency types. These fields are stored internally with 2 decimals, irrespective of the currency used. It can be easily done using write statement if you want to round the amount field in the report. How to do it if you want to round it store it as a currency amount field itself. This is a problem in SAP query reports. In my case the user wanted to amount fields to appear rounded to nearest integer. SAP has some built-in-functions like ceil, floor but they can not be used as it is, due to the fact that the amount is stored internally with 2 decimals. Most of the currencies are with 2 decimals and it is still not a problem. This can be easily achieved by the following operation. A constant need to be defined with value 0.5. rounding is achieved by amount = floor( amount + constant ). How can this be done for currencies with other than 2 decimals. For example, Bahraini Dinar, Omani Riyal, Japanese Yen. The concept is same, but with an additional conversion. There is a BAPI function module to convert currency fields to external and vice the versa. Using these FMs convert the amount to first external format. Apply the formula as mentioned above and again using the BAPI FM convert it back to internal format.