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	$18.96	12.146%	$21.2629	$21.26	$21.25	$21.30
Purchase #2	$61.38	6.150%	$65.1549	$65.15	$65.15	$65.20
Purchase #3	$59.38	4.528%	$62.0687	$62.07	$62.05	$62.10
Purchase #4	$53.40	4.662%	$55.8895	$55.89	$55.90	$55.90
Purchase #5	$102.58	8.476%	$111.2747	$111.27	$111.25	$111.30
Purchase #6	$152.97	8.349%	$165.7415	$165.74	$165.75	$165.70
Purchase #7	$6.77	8.286%	$7.331	$7.33	$7.35	$7.30
7 purchase totals =	$455.44		$488.7232	$488.71	$488.70	$488.80