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	$99.83	11.795%	$111.6049	$111.60	$111.60	$111.60
Purchase #2	$139.95	11.408%	$155.9155	$155.92	$155.90	$155.90
Purchase #3	$55.31	9.413%	$60.5163	$60.52	$60.50	$60.50
Purchase #4	$90.27	4.772%	$94.5777	$94.58	$94.60	$94.60
Purchase #5	$86.89	8.258%	$94.0654	$94.07	$94.05	$94.10
Purchase #6	$203.44	3.515%	$210.5909	$210.59	$210.60	$210.60
Purchase #7	$46.60	9.146%	$50.862	$50.86	$50.85	$50.90
7 purchase totals =	$722.29		$778.1327	$778.14	$778.10	$778.20