the irs first focused on high-income individuals and larger corporations, but now the service is stepping up its audits of small businesses. in 2005, audits of the roughly 5.7 million small businesses the irs recognizes to be organized as corporations increased significantly, with 17,867 audits, up from 7,294 a year earlier. meanwhile, audits of corporations with assets over $10 million also increased only 14% in 2005, to 10,878. irs chief mark everson says he expects 2006 to reach an even greater rate of small-business enforcement. more at businessweek…