If you did renovations that did not require a permit, the biggest "penalty" would be on your taxes. If you did the renovations without a permit and one or more was required, I have seen where they require you to pay for a permit (even though it is after the fact),and inspect to be sure the work has been done correctly. If the work is not completed within the rules and safely done, they can have you deconstruct after the fact. (no joke). I am not sure about what kind of fines may be involved, but again, I would think that the worst scenario would be the removal of the addition if done against the rules and regulations. I am not sure about a fine, I would suggest you contact the county building and permit offices http://(www.coj.net) and ask someone in the permitting office to be sure that you are receiving the correct information.
If you are selling you may have over improved. If that is the situation then your lose would be the amount that you over improved. If it is just the city appraiser then the difference will reflect in your revised properety taxes. I live in your zip code. I would be happy to take a look and give you an idea what you may be looking at. Give me a call at 904-463-4264