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	$38.68	3.653%	$40.093	$40.09	$40.10	$40.10
Purchase #2	$13.83	13.487%	$15.6953	$15.70	$15.70	$15.70
Purchase #3	$196.58	4.705%	$205.8291	$205.83	$205.85	$205.80
Purchase #4	$11.38	12.228%	$12.7715	$12.77	$12.75	$12.80
Purchase #5	$228.45	9.382%	$249.8832	$249.88	$249.90	$249.90
Purchase #6	$100.84	10.446%	$111.3737	$111.37	$111.35	$111.40
Purchase #7	$56.72	7.310%	$60.8662	$60.87	$60.85	$60.90
7 purchase totals =	$646.48		$696.5120	$696.51	$696.50	$696.60