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	$68.96	8.152%	$74.5816	$74.58	$74.60	$74.60
Purchase #2	$26.64	11.871%	$29.8024	$29.80	$29.80	$29.80
Purchase #3	$155.31	6.749%	$165.7919	$165.79	$165.80	$165.80
Purchase #4	$83.64	10.806%	$92.6781	$92.68	$92.70	$92.70
Purchase #5	$57.42	3.222%	$59.2701	$59.27	$59.25	$59.30
Purchase #6	$115.53	10.295%	$127.4238	$127.42	$127.40	$127.40
Purchase #7	$92.52	5.205%	$97.3357	$97.34	$97.35	$97.30
7 purchase totals =	$600.02		$646.8836	$646.88	$646.90	$646.90