Tokyo stocks ended mixed Tuesday, as selling ahead of key central bank meetings in the United States and Japan this week erased earlier gains driven by strength in heavyweight semiconductor-related shares. The 225-issue Nikkei Stock Average ended up 96.63 points, or 0.25 percent, from Monday at 39,134.79. The broader Topix index finished 5.69 points, or 0.20 percent, lower at 2,776.80. On the top-tier Prime Market, gainers were led by machinery, precision instrument and nonferrous metal shares. The main decliners were marine transportation, securities house and air transportation shares. The U…