Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$39.35	3.828%	$40.8563	$40.86	$40.85	$40.90
Purchase #2	$43.60	10.355%	$48.1148	$48.11	$48.10	$48.10
Purchase #3	$125.79	11.148%	$139.8131	$139.81	$139.80	$139.80
Purchase #4	$24.55	10.683%	$27.1727	$27.17	$27.15	$27.20
Purchase #5	$90.33	11.715%	$100.9122	$100.91	$100.90	$100.90
Purchase #6	$75.96	6.271%	$80.7235	$80.72	$80.70	$80.70
Purchase #7	$138.30	11.509%	$154.2169	$154.22	$154.20	$154.20
7 purchase totals =	$537.88		$591.8095	$591.80	$591.70	$591.80