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	$152.25	9.350%	$166.4854	$166.49	$166.50	$166.50
Purchase #2	$238.96	13.624%	$271.5159	$271.52	$271.50	$271.50
Purchase #3	$247.32	11.245%	$275.1311	$275.13	$275.15	$275.10
Purchase #4	$29.58	9.278%	$32.3244	$32.32	$32.30	$32.30
Purchase #5	$247.62	12.471%	$278.5007	$278.50	$278.50	$278.50
Purchase #6	$39.25	8.766%	$42.6907	$42.69	$42.70	$42.70
Purchase #7	$238.84	13.684%	$271.5229	$271.52	$271.50	$271.50
7 purchase totals =	$1,193.82		$1,338.1711	$1,338.17	$1,338.15	$1,338.10