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	$104.32	7.172%	$111.8018	$111.80	$111.80	$111.80
Purchase #2	$51.45	4.271%	$53.6474	$53.65	$53.65	$53.60
Purchase #3	$182.69	12.649%	$205.7985	$205.80	$205.80	$205.80
Purchase #4	$127.32	12.140%	$142.7766	$142.78	$142.80	$142.80
Purchase #5	$20.70	13.338%	$23.461	$23.46	$23.45	$23.50
Purchase #6	$124.32	6.787%	$132.7576	$132.76	$132.75	$132.80
Purchase #7	$204.52	12.870%	$230.8417	$230.84	$230.85	$230.80
7 purchase totals =	$815.32		$901.0846	$901.09	$901.10	$901.10