I couldn't find one complete source, but document from Ministry of Foreign Affair about VITEM I says in point 18.:
Upon arrival in Brazil, bearers of a Temporary Visa I must register with the Brazilian Federal Police Department (Delegacia de Estrangeiros) within 30 days from date of arrival.
Also this Consulate's website (Houston in particular, but information on others is similar) says
Failing to register in time will result in daily fines. If you need to be registered, it will be written on the notes on your visa label.
So it also seems you should make sure on your visa label that you indeed must register. On my visa it says explicitly that I have to register in 30 days.
I can't find information about the amount of the fine for failing to register in Brazilian sources. If you don't prolong visa and stay over 90 days, the fine is 8,25 BRL / day, up to 827,75 BRL, according to Federal Police Website (in Portuguese), so I'm expecting it's similar amount, I'll update the answer if I find this info.
From experience of my friends and mentioned websites I know that on the border you shouldn't have any problems, they will not imprison you or ban from entering the country again, you would only have to pay the fine.