I am using the Amazon Marketplace Web Service Order API:
Is there a transaction summary API for Amazon?
I want to calculate Amazon fees accurately:
Amazon Fees (Variable closing fee, commission) Shipping service fees
Is there an API where I can obtain these exact amounts?
Yes, you can get this information by retrieving Settlement Reports using the MWS Reports API. They are available in XML or flat file format.
Here is some general information about the Settlement Reports: http://www.amazon.com/gp/help/customer/display.html?nodeId=200253140
And here are the different MWS report type enumerations for Settlement Reports: http://docs.developer.amazonservices.com/en_US/reports/Reports_ReportType.html#ReportTypeCategories__SettlementReports