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	$158.42	6.244%	$168.3117	$168.31	$168.30	$168.30
Purchase #2	$138.72	9.832%	$152.359	$152.36	$152.35	$152.40
Purchase #3	$111.72	9.841%	$122.7144	$122.71	$122.70	$122.70
Purchase #4	$177.92	12.381%	$199.9483	$199.95	$199.95	$199.90
Purchase #5	$205.29	13.309%	$232.612	$232.61	$232.60	$232.60
Purchase #6	$82.70	8.223%	$89.5004	$89.50	$89.50	$89.50
Purchase #7	$87.47	3.748%	$90.7484	$90.75	$90.75	$90.70
7 purchase totals =	$962.24		$1,056.1942	$1,056.19	$1,056.15	$1,056.10