Tokyo stocks fell slightly Tuesday morning, as investors locked in recent gains after the Nikkei index rallied for six consecutive days to reach highs last seen in early 1990. The 225-issue Nikkei Stock Average dropped 109.73 points, or 0.31 percent, from Monday to 35,792.06. The broader Topix index was down 12.31 points, or 0.49 percent, at 2,512.29. The U.S. dollar firmed to the lower 146 yen range in Tokyo as the yen was sold amid the view that the Bank of Japan will not move to normalize its ultraloose monetary policy this month, as it intends to support the economy following a recent dest…