TOUGHER TIMES FOR THE TAXMAN. The Internal Revenue Service was embarrassed last summer by congressional hearings that unearthed a string of cases involving high-level misconduct and cover-ups inside the agency. Now the new IRS commissioner, Fred Goldberg Jr., has come up with a plan that should make it harder for such episodes to recur. Henceforth, allegations of misconduct against high-ranking IRS agents will be probed by the Treasury Department's inspector general instead of the tax agency's own investigators.