Depending on your business legal status, in my country you are able to declare an average income and pay a trimestrial tax according to that. This way you know that you have to pay a fixed tax.
The good: if, in a month / trimester you earn a bit more, you get to save some money.
The bad: if, in a month/trimester you earn a bit lower than you declared, you still have to pay taxes for the full declared ammount.
P.S If your income is below a certain ammount, it's not compulsory to hire an accountant.