As a result of widespread destruction of its infrastructure, Mozambique is an inexpensive destination. The most readily accepted currencies are US dollars and South African rands. The best places to change money are the private bureaux in Maputo, which give better rates than the banks.
Local banks have branches in most cities.
Changing money on the street is not safe anywhere. In general, tipping isn't expected, and you may find yourself having to explain that you really don't want your change. Things are a little different in Maputo, where prolonged exposure to foreign tourists and expats has given the locals a taste for tips. In general, the more upscale the place the higher the rate. Bargaining, especially in the open air markets, is commonplace.