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	$10.42	11.233%	$11.5905	$11.59	$11.60	$11.60
Purchase #2	$144.66	9.631%	$158.5922	$158.59	$158.60	$158.60
Purchase #3	$44.73	13.654%	$50.8374	$50.84	$50.85	$50.80
Purchase #4	$248.89	13.242%	$281.848	$281.85	$281.85	$281.80
Purchase #5	$233.77	7.716%	$251.8077	$251.81	$251.80	$251.80
Purchase #6	$177.62	4.592%	$185.7763	$185.78	$185.80	$185.80
Purchase #7	$80.62	9.733%	$88.4667	$88.47	$88.45	$88.50
7 purchase totals =	$940.71		$1,028.9188	$1,028.93	$1,028.95	$1,028.90