Rounding off amount on invoices created in SD

I want to round customers invoices created in SAP-SD. I have added a new Condition Type to our Pricing Procedure, so that we are now able to 'manually' enter the rounding. What I would like to know is whether there is any way to calculate this rounding 'automatically'? and how?

Is there any user-exit, OSS note, etc. I can implement? Has anybody found this issue in another SAP implementation?