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	$59.93	7.218%	$64.2557	$64.26	$64.25	$64.30
Purchase #2	$189.42	4.855%	$198.6163	$198.62	$198.60	$198.60
Purchase #3	$121.81	8.133%	$131.7168	$131.72	$131.70	$131.70
Purchase #4	$239.66	7.422%	$257.4476	$257.45	$257.45	$257.40
Purchase #5	$215.89	10.492%	$238.5412	$238.54	$238.55	$238.50
Purchase #6	$161.89	6.605%	$172.5828	$172.58	$172.60	$172.60
Purchase #7	$7.34	10.720%	$8.1268	$8.13	$8.15	$8.10
7 purchase totals =	$995.94		$1,071.2872	$1,071.30	$1,071.30	$1,071.20