Currency fields must be attached in ddic (or field catalog for ALV) to a currency field, which will define number of decimal places, and adjust conversion at display. You cannot just move the received field to the currency amount field, but must take currency code (number of decimal) into consideration (Look in online help for BAPI_CURRENCY_CONV_TO_INTERNAL)
Hint: when no currency code attached to currency amount, SAP displays 2 decimal places.
Regards,
Raymond