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	$30.72	6.490%	$32.7137	$32.71	$32.70	$32.70
Purchase #2	$67.98	13.497%	$77.1553	$77.16	$77.15	$77.20
Purchase #3	$49.65	7.613%	$53.4299	$53.43	$53.45	$53.40
Purchase #4	$250.82	8.224%	$271.4474	$271.45	$271.45	$271.40
Purchase #5	$176.96	9.472%	$193.7217	$193.72	$193.70	$193.70
Purchase #6	$85.40	5.486%	$90.085	$90.09	$90.10	$90.10
Purchase #7	$101.49	4.820%	$106.3818	$106.38	$106.40	$106.40
7 purchase totals =	$763.02		$824.9348	$824.94	$824.95	$824.90