Tax is the most obvious of quite a few areas where good, pro-active accounting can save you money, not just cost you.
Getting your tax right (meaning, not paying more than you are legally obliged to) will make your life a lot smoother and less stressful. Time spent arguing with the ATO is totally negative, unproductive and wasteful.
Just as important is to plan your tax payments, as they can have a significant impact on your cash flow management.