While technically it might be possible to save into Nikon's ND2 format, it is typically recorded by digital microscopes and not meant to store graphics content. You can find graphics viewers/editors that support working with .nd2 files, but it is likely that saving random raster/bitmap image to this format, i.e. tiff to nd2 conversion, will be useless, considering that digital RAW contain special metadata recorded by the devices/cameras.
Updated: August 15, 2023