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	$155.31	10.198%	$171.1485	$171.15	$171.15	$171.10
Purchase #2	$87.67	3.527%	$90.7621	$90.76	$90.75	$90.80
Purchase #3	$127.26	13.206%	$144.066	$144.07	$144.05	$144.10
Purchase #4	$55.52	13.313%	$62.9114	$62.91	$62.90	$62.90
Purchase #5	$211.66	4.138%	$220.4185	$220.42	$220.40	$220.40
Purchase #6	$46.59	13.643%	$52.9463	$52.95	$52.95	$52.90
Purchase #7	$56.68	12.409%	$63.7134	$63.71	$63.70	$63.70
7 purchase totals =	$740.69		$805.9662	$805.97	$805.90	$805.90