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	$25.80	10.358%	$28.4724	$28.47	$28.45	$28.50
Purchase #2	$105.62	5.245%	$111.1598	$111.16	$111.15	$111.20
Purchase #3	$209.75	6.762%	$223.9333	$223.93	$223.95	$223.90
Purchase #4	$235.75	7.404%	$253.2049	$253.20	$253.20	$253.20
Purchase #5	$45.52	13.312%	$51.5796	$51.58	$51.60	$51.60
Purchase #6	$88.50	6.588%	$94.3304	$94.33	$94.35	$94.30
Purchase #7	$10.77	10.433%	$11.8936	$11.89	$11.90	$11.90
7 purchase totals =	$721.71		$774.5740	$774.56	$774.60	$774.60