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	$10.32	6.297%	$10.9699	$10.97	$10.95	$11.00
Purchase #2	$199.60	11.584%	$222.7217	$222.72	$222.70	$222.70
Purchase #3	$228.70	6.610%	$243.8171	$243.82	$243.80	$243.80
Purchase #4	$236.64	4.542%	$247.3882	$247.39	$247.40	$247.40
Purchase #5	$172.86	7.300%	$185.4788	$185.48	$185.50	$185.50
Purchase #6	$118.98	10.250%	$131.1755	$131.18	$131.20	$131.20
Purchase #7	$153.97	10.425%	$170.0214	$170.02	$170.00	$170.00
7 purchase totals =	$1,121.07		$1,211.5726	$1,211.58	$1,211.55	$1,211.60