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	$132.57	8.462%	$143.7881	$143.79	$143.80	$143.80
Purchase #2	$223.66	4.288%	$233.2505	$233.25	$233.25	$233.30
Purchase #3	$129.76	10.103%	$142.8697	$142.87	$142.85	$142.90
Purchase #4	$9.43	11.298%	$10.4954	$10.50	$10.50	$10.50
Purchase #5	$91.39	12.566%	$102.8741	$102.87	$102.85	$102.90
Purchase #6	$123.69	5.766%	$130.822	$130.82	$130.80	$130.80
Purchase #7	$120.47	11.747%	$134.6216	$134.62	$134.60	$134.60
7 purchase totals =	$830.97		$898.7214	$898.72	$898.65	$898.80