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	$85.75	5.398%	$90.3788	$90.38	$90.40	$90.40
Purchase #2	$143.91	9.784%	$157.9902	$157.99	$158.00	$158.00
Purchase #3	$99.31	6.113%	$105.3808	$105.38	$105.40	$105.40
Purchase #4	$15.46	7.635%	$16.6404	$16.64	$16.65	$16.60
Purchase #5	$247.93	11.833%	$277.2676	$277.27	$277.25	$277.30
Purchase #6	$60.92	10.172%	$67.1168	$67.12	$67.10	$67.10
Purchase #7	$129.52	12.548%	$145.7722	$145.77	$145.75	$145.80
7 purchase totals =	$782.80		$860.5468	$860.55	$860.55	$860.60