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	$52.74	5.226%	$55.4962	$55.50	$55.50	$55.50
Purchase #2	$64.50	4.581%	$67.4547	$67.45	$67.45	$67.50
Purchase #3	$241.76	7.286%	$259.3746	$259.37	$259.35	$259.40
Purchase #4	$74.74	11.801%	$83.5601	$83.56	$83.55	$83.60
Purchase #5	$163.57	5.559%	$172.6629	$172.66	$172.65	$172.70
Purchase #6	$19.52	8.286%	$21.1374	$21.14	$21.15	$21.10
Purchase #7	$193.70	7.769%	$208.7486	$208.75	$208.75	$208.70
7 purchase totals =	$810.53		$868.4345	$868.43	$868.40	$868.50