Yes, all electricity tariffs are regulated by NERSA. You can view them on their website under Electricity - > Tariffs.
Each municipality has a different size, population, budget, infrastructure, maintenance, labour, free electricity allowance etc, so the costs are all different. That is why their tariffs are different. But the price they pay Eskom is the same. Municipalities also use electricity tariffs to generate their most profits, in order to subsidise other services (yes, it is crazy, but electricity is the easiest money to collect from residents).
For all these reasons, electricity is a cash cow and a way to force people to pay for municipal services. The increases each year are usually similar across muni's though, as NERSA tries to keep increases to a minimum.