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	$220.48	6.407%	$234.6062	$234.61	$234.60	$234.60
Purchase #2	$133.50	7.609%	$143.658	$143.66	$143.65	$143.70
Purchase #3	$179.93	5.687%	$190.1626	$190.16	$190.15	$190.20
Purchase #4	$222.37	7.195%	$238.3695	$238.37	$238.35	$238.40
Purchase #5	$239.47	3.368%	$247.5353	$247.54	$247.55	$247.50
Purchase #6	$42.55	6.390%	$45.2689	$45.27	$45.25	$45.30
Purchase #7	$206.51	5.488%	$217.8433	$217.84	$217.85	$217.80
7 purchase totals =	$1,244.81		$1,317.4438	$1,317.45	$1,317.40	$1,317.50