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	$44.58	12.489%	$50.1476	$50.15	$50.15	$50.10
Purchase #2	$193.72	5.122%	$203.6423	$203.64	$203.65	$203.60
Purchase #3	$98.29	10.401%	$108.5131	$108.51	$108.50	$108.50
Purchase #4	$39.78	4.111%	$41.4154	$41.42	$41.40	$41.40
Purchase #5	$73.51	9.381%	$80.406	$80.41	$80.40	$80.40
Purchase #6	$231.75	10.113%	$255.1869	$255.19	$255.20	$255.20
Purchase #7	$198.97	12.211%	$223.2662	$223.27	$223.25	$223.30
7 purchase totals =	$880.60		$962.5775	$962.59	$962.55	$962.50