The issue of tipping is very delicate. Firstly it isn't mandatory in principle but inevitably it is the strong custom in especially tourism, we must follow, based on the assessment of customer satisfaction with human services, having made good services.
According to the travel tradition, the fact to tip the servants such: porters in hotels, pedaling pedicab, rowers, especially the guides and driver - assist, is very necessary and practical according to a scale to a minimum. This presents a knowledge of the culture and human behavior between Clients/ Servers.
Certainly, they are very poorly paid compared to what you see at home.
It isn't advisable to give too small tips. It is better to give nothing than to give too small fee that can offend and this bothers you durantle trip.
Concerning the gratuity for guides, provide for about 3 to 4 Euros/ day/ traveler if you are really happy with their services. When the group has several participants (6 or more) every traveler can give from February to March Euros.
Count the half for the driver (otherwise you vexerez the guide!). Small tip for the porters also hotels.
Regarding the pedicabs, stick to the agreed price. A little extra tip can only be linked to his kindness. In principle, no tip at the bars and in restaurants. Leave one is a matter of personal and human appreciation.
The practice offerings
You see énorment Vietnamese pilgrims bring and give offerings and leave around some VND on plates before statues or put them in a box of the donation in the temples and pagodas. Here there is no tip, but a contribution to worship, prayers, maintenance of the premises, etc. It is also a very good custom in traditional thoughts of Vietnamese now more offerings to give more and receive prayer after either for himself or for his children and descendants. It is very fashionable to leave some VND in the box.