Exchange rate rounding off.

Hi

Please help me to solve the below issue.

1. We are using SPOT rate to convert foreign currency into local currency.

2. We collect advance payment from customer say on 1.9.2010 and we raise a payment invoice at the SPOT rate on 1.9.2010.

And collect the balance payment on 10.09.2010 at the SPOT rate on 10.09.2010.

3. We will add the SPOT rates of both the dates and create final billing to customers by rounding off the exchange rates.

The problem is that, SAP supports to round off upto three decimals but the business want it to be rounded off to five decimals.

We are doing this through coding and not through configuration.

Could any one help me how to round off the SPOT rate upto to 5 decimals.

regards

Hari