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	$247.98	3.554%	$256.7932	$256.79	$256.80	$256.80
Purchase #2	$218.41	4.144%	$227.4609	$227.46	$227.45	$227.50
Purchase #3	$20.25	13.201%	$22.9232	$22.92	$22.90	$22.90
Purchase #4	$196.69	7.106%	$210.6668	$210.67	$210.65	$210.70
Purchase #5	$133.98	8.143%	$144.89	$144.89	$144.90	$144.90
Purchase #6	$136.49	4.756%	$142.9815	$142.98	$143.00	$143.00
Purchase #7	$128.40	4.819%	$134.5876	$134.59	$134.60	$134.60
7 purchase totals =	$1,082.20		$1,140.3032	$1,140.30	$1,140.30	$1,140.40