I didnt vote in local council elections once because I didnt realise it was compulsory (dumb I know, but I was very young at the time). I wrote a letter trying to get out of it. Then, as I had moved house I didnt get the letter saying that I still had to pay the fine. Because I didnt pay the fine by the due date, interest got applied and when they eventually found my new address the fine was double the original amount. Expensive lesson that one, but I always find time to vote now.
So be aware if you dont pay it, you may well get penalised for not paying it and the fine will be even more.