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	$42.53	13.491%	$48.2677	$48.27	$48.25	$48.30
Purchase #2	$114.70	10.822%	$127.1128	$127.11	$127.10	$127.10
Purchase #3	$86.86	9.522%	$95.1308	$95.13	$95.15	$95.10
Purchase #4	$53.77	8.555%	$58.37	$58.37	$58.35	$58.40
Purchase #5	$54.69	3.447%	$56.5752	$56.58	$56.60	$56.60
Purchase #6	$16.89	8.121%	$18.2616	$18.26	$18.25	$18.30
Purchase #7	$14.26	6.395%	$15.1719	$15.17	$15.15	$15.20
7 purchase totals =	$383.70		$418.8900	$418.89	$418.85	$419.00