Tipping is western culture. But it is being a culture in Nepal as well, especially in the travel sector. A guide and a porter will be happy if they get a tip. But the amount of tip is not set in Nepal. You can give a tip as per your preference depending on your satisfaction level. Except for the guide and porter, you do not need to give a tip to the driver or hotel staff. Because it is charged already in a bill. However, it is up to you whether to provide a tip or not.