Zimbabwe uses the United States dollar and the South African rand.  The local currency the Zimbabwean Dollar was taken out of circulation in 2008 when inflation made even a one hundred trillion dollar note worthless.

The Botswana Pula, British Pounds and Euros are also legal tender along with a number of other currencies such as the AU$.  However only the $ and to some extent SA Rand are readily accepted in most shops.

In Bulawayo and the rest of the Matabeleland the rand is actually prefered to the dollar.  Some supermarkets have cross rates for different currencies displayed and will accept them and give you change in dollars.  Change  for amounts smaller than a dollar is often hard to come by and you may be offered sweets instead.  Otherwise change is given in South African rand at a notional rate of R10 to $1 or in 'Bond Coins' which are a local invention and equivalant to the same amount in American cent coins.  It is unlikely that you will get the exact change and being let off 5 to 10 cents or losing the same amount in a transaction is quite common (unless you really want a bubble gum).  If you have cent coins from the States you will not find them easy to use for some reason.

ATMs are found in most of the main towns and cities and quite a few take Visa cards and some take Mastercard.  Barclays and Standard Chartered have a large network of ATMs but some other local banks will also take foreign visa cards.

You can change money at most large banks though the rates are not brilliant.

Dollar notes tend to become very dirty quickly so you will have to get used to some rather unpleasant looking money in your wallet/purse/pocket book.