We know they're all scams but this person actually spent time, did the math, and sat in on these "auctions" to give you all the details:
http://onlinescamwebsites.com/how-do-penny-auctions-work/ The author made a comparison to online casinos but I beg to differ; People throw their money away on online casinos but THOSE SITES are far more honest about what they ARE... While online casinos are illegal (at least in the US), penny auction sites are perfectly legal while doing similar yet arguably even worse things.