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	$11.60	12.359%	$13.0336	$13.03	$13.05	$13.00
Purchase #2	$145.86	8.634%	$158.4536	$158.45	$158.45	$158.50
Purchase #3	$174.87	13.468%	$198.4215	$198.42	$198.40	$198.40
Purchase #4	$136.48	9.143%	$148.9584	$148.96	$148.95	$149.00
Purchase #5	$55.95	9.865%	$61.4695	$61.47	$61.45	$61.50
Purchase #6	$104.87	6.672%	$111.8669	$111.87	$111.85	$111.90
Purchase #7	$145.49	6.106%	$154.3736	$154.37	$154.35	$154.40
7 purchase totals =	$775.12		$846.5771	$846.57	$846.50	$846.70