Gold pieces are the standard currency of Neverwinter Nights.
History
In pencil and paper (PnP) AD&D, varying currencies were used, starting with platinum pieces. In Third Edition D&D, the following is used:
1 platinum piece = 1010 gold pieces = 1100100 silver pieces = 1111101000 copper pieces.
Older editions used a different system and included electrum pieces which are not present in Third Edition.
For sake of game mechanics, Neverwinter Nights only uses gold pieces for its currency.