SAN FRANCISCO -No. 756 is going to auction. Barry Bonds' record-breaking home run ball will be sold online, and fortunate fan Matt Murphy figures to be a half-million dollars richer.The 21-year-old New York man said Tuesday he had no choice but to sell the ball - several people told him he would be taxed on the souvenir just for holding on to it."It wasn't hard. It was simple math. I'm upset by the decision I had to make," Murphy said. "I wanted to keep it. I'm young. I don't have the bank account. ... It would have cost me a lot more to keep it."Bonds broke Hank Aaron's record of 755 with a shot into the right-field seats on Aug. 7 against the Washington Nationals."This is the most historic baseball ever to be sold," said David Kohler, president of SCP Auctions.The ball from Bonds' 755th home run hit Aug. 4 in San Diego also will be for sale on the site. The same company sold the balls from Bonds' 700th homer and No. 715 that passed Babe Ruth for second place last season.Everyone involved hopes the buyer of the historic balls is willing to at least share them for a period of time - if not donate them altogether - with the Hall of Fame in Cooperstown, N.Y."I really hope the person who does buy it is in position to loan it," Murphy said, a security guard close by him during a news conference at a restaurant near the ballpark. "Two weeks ago, history was made. I was lucky enough to be in the house."Murphy plans to share at least some of the proceeds with a friend who attended the Giants game with him. They were in town for a brief stopover on a trip to Australia when Murphy wound up with the lucky prize.Murphy left the ball in safekeeping with a bank in San Francisco during his more than weeklong trip to Australia. He returned to the Bay Area on Sunday to make arrangements for the ball.Bonds has said he believes his home run balls belong to the fans."I haven't spoken with Barry," said Murphy, who is considering attending business school in New York City. "I would like to meet him."The City of San Francisco will honor Bonds in a public ceremony Friday.