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	$143.65	3.828%	$149.1489	$149.15	$149.15	$149.10
Purchase #2	$231.43	8.528%	$251.1664	$251.17	$251.15	$251.20
Purchase #3	$13.43	10.789%	$14.879	$14.88	$14.90	$14.90
Purchase #4	$53.66	11.210%	$59.6753	$59.68	$59.70	$59.70
Purchase #5	$68.78	4.765%	$72.0574	$72.06	$72.05	$72.10
Purchase #6	$177.94	12.831%	$200.7715	$200.77	$200.75	$200.80
Purchase #7	$58.56	6.858%	$62.576	$62.58	$62.60	$62.60
7 purchase totals =	$747.45		$810.2745	$810.29	$810.30	$810.40