Procurement of books in India where price is in a currency other than INR is typically governed by GOC (Good offices committee) rates. See http://fpbai.org/goc-rates/ This rate is not necessarily as per the prevailing (short term) FOREX rates. Further it is required to maintain a history of the GOC rates for disbursal and payment of invoices.
I think this is a partial dupclicate to each of those bugs: * Bug 7571 - Maintain exchange rate history * Bug 3758 - Automatic update of exchange rates Koha doesn't care what rates you use, so using the GOC rates should be possible, but it might need to be taken into account if updating rates is automated as an additional option (depending on the availability of web services) *** This bug has been marked as a duplicate of bug 7571 ***