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	$178.82	3.399%	$184.8981	$184.90	$184.90	$184.90
Purchase #2	$55.71	12.224%	$62.52	$62.52	$62.50	$62.50
Purchase #3	$89.97	4.698%	$94.1968	$94.20	$94.20	$94.20
Purchase #4	$99.28	6.125%	$105.3609	$105.36	$105.35	$105.40
Purchase #5	$229.92	10.345%	$253.7052	$253.71	$253.70	$253.70
Purchase #6	$37.90	7.164%	$40.6152	$40.62	$40.60	$40.60
Purchase #7	$65.94	13.185%	$74.6342	$74.63	$74.65	$74.60
7 purchase totals =	$757.54		$815.9304	$815.94	$815.90	$815.90