Shares of Roundy?s stock began trading on the New York Stock Exchange on Wednesday and ended the day up 50 cents, at $9 a share. The Milwaukee grocery company offered 19.2 million shares of common stock in its initial public offering on the New York Stock Exchange, under the symbol RNDY. Shares were priced at $8.50, which was below the $10 to $12 price projected in a company document filed with federal regulators in January. That signifies “tepid response from the marketplace” to the offering, said Jim Seward, associate professor at the UW-Madison School of Business and faculty director of the Nicholas Center for Corporate Finance and Investment Banking.