Yes, tipping is common in South Africa, including Randburg. In restaurants, it is customary to tip about 10-15% of the total bill. However, always make sure that the service charge is not already included. The tip is an important part of the restaurant staff's income, and if you were satisfied with the service, it is definitely welcome. It is usually paid in cash directly to the waiter. Remember that tipping is a matter of personal discretion.