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	$63.70	12.677%	$71.7752	$71.78	$71.80	$71.80
Purchase #2	$52.85	5.102%	$55.5464	$55.55	$55.55	$55.50
Purchase #3	$209.79	9.444%	$229.6026	$229.60	$229.60	$229.60
Purchase #4	$177.39	9.782%	$194.7423	$194.74	$194.75	$194.70
Purchase #5	$241.35	12.241%	$270.8937	$270.89	$270.90	$270.90
Purchase #6	$63.39	11.482%	$70.6684	$70.67	$70.65	$70.70
Purchase #7	$95.95	4.293%	$100.0691	$100.07	$100.05	$100.10
7 purchase totals =	$904.42		$993.2977	$993.30	$993.30	$993.30