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	$37.86	12.241%	$42.4944	$42.49	$42.50	$42.50
Purchase #2	$248.25	12.368%	$278.9536	$278.95	$278.95	$279.00
Purchase #3	$119.67	10.806%	$132.6015	$132.60	$132.60	$132.60
Purchase #4	$205.75	5.512%	$217.0909	$217.09	$217.10	$217.10
Purchase #5	$37.87	4.848%	$39.7059	$39.71	$39.70	$39.70
Purchase #6	$83.90	6.705%	$89.5255	$89.53	$89.55	$89.50
Purchase #7	$187.57	3.692%	$194.4951	$194.50	$194.50	$194.50
7 purchase totals =	$920.87		$994.8669	$994.87	$994.90	$994.90