By Amanda Cooper LONDON (Reuters) -The U.S. dollar held firm on Tuesday ahead of a likely U.S. government shutdown that could disrupt the release of the monthly jobs report this week, while the Australian dollar was the top-performing major currency of the day after the central bank sounded a cautious note on inflation. Investor focus is on the impending U.S. shutdown. Government funding expires at midnight on Tuesday (0400 GMT) unless Republicans and Democrats agree to a last-minute temporary spending ...