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	$45.78	11.388%	$50.9934	$50.99	$51.00	$51.00
Purchase #2	$66.48	10.391%	$73.3879	$73.39	$73.40	$73.40
Purchase #3	$22.58	9.150%	$24.6461	$24.65	$24.65	$24.60
Purchase #4	$140.25	13.506%	$159.1922	$159.19	$159.20	$159.20
Purchase #5	$154.83	7.786%	$166.8851	$166.89	$166.90	$166.90
Purchase #6	$20.83	3.314%	$21.5203	$21.52	$21.50	$21.50
Purchase #7	$106.43	4.732%	$111.4663	$111.47	$111.45	$111.50
7 purchase totals =	$557.18		$608.0913	$608.10	$608.10	$608.10