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	$7.66	3.356%	$7.9171	$7.92	$7.90	$7.90
Purchase #2	$246.45	6.693%	$262.9449	$262.94	$262.95	$262.90
Purchase #3	$200.83	10.796%	$222.5116	$222.51	$222.50	$222.50
Purchase #4	$43.70	11.435%	$48.6971	$48.70	$48.70	$48.70
Purchase #5	$237.98	7.821%	$256.5924	$256.59	$256.60	$256.60
Purchase #6	$129.46	13.408%	$146.818	$146.82	$146.80	$146.80
Purchase #7	$177.95	9.420%	$194.7129	$194.71	$194.70	$194.70
7 purchase totals =	$1,044.03		$1,140.1940	$1,140.19	$1,140.15	$1,140.10