Sharing meal costs with your partners is not part of Vietnamese culture. If you are the host of a party, it means that you make all invitations, planning for the menu as well as the restaurant and then you pay for the bill. In particular in business sections, if you are guests, feel easy about bill payment because certainly the next time it is your turn to repay the kindness.
Meanwhile, when gathering with friends or colleagues in general, Vietnamese people would like to share the money with each other if the bills are massive. However, restaurants rarely have separate bills for each person, so it does not matter if you order a cocktail or a lemon juice, it will be equally divided at the end.
There is a way, perhaps, to eliminate financial stress and create a great money sharing relationship. If some close friends hang out together, it is common that one is willing to take charge of the bill and the next time will be others' turns. In the case of dating couples, it maybe different from Western culture. Vietnamese males always prefer to take care of payment while females rarely do this.
In Viet Nam culture, men who pay for all are considered more generous and gallant. This attitude sometimes causes conflicts within relationships and not be representative of Vietnamese culture as a whole. Do not worry about this issue because the most essential point is to have fun with your friends and partners.