Unless you are selling over a certain number of dozen a week, you don't have to worry with cartons too much. Try contacting one of the folks listed in the first link and see what the number of dozen is. I can't remember what it is.
http://ncagr.gov/fooddrug/food/egglaw.htm
http://ncagr.gov/fooddrug/food/eggregs.htm
http://ncagr.gov/fooddrug/food/egglaw.htm
http://ncagr.gov/fooddrug/food/eggregs.htm