From Otto L. Bettman's book "The Good Old Days--They Were Terrible":"In New York drunks were confined in the Asylum for Inebriates on Blackwell's Island. Released after a few days of abstinence, they often went on a new binge, and, incarcerated again, became known as 'rounders'." This might not be the only source of the word, but it's one, and in view of the justice, and social, system,probably referrred to a path trodden by many poor guys, black and white.