Hi Shyam
This is just a case of difference in the code at two different places. I read the code of the functional module and find that it is using the standard rounding off feature provided by SAP for numbers. there is no additional rounding off mentioned in the code. I am not sure which module gets called in the PO although.
You can also your ABAPer to modify the functional module so that the values in the PO and idoc match (small change needed)
Moreover, you can modify the structure of your idoc and load the price from the PO tables directly or some other Zmodule which will make the values identical.
Regards
Vivek Singh