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	$105.53	5.682%	$111.5262	$111.53	$111.55	$111.50
Purchase #2	$108.74	12.629%	$122.4728	$122.47	$122.45	$122.50
Purchase #3	$66.63	10.128%	$73.3783	$73.38	$73.40	$73.40
Purchase #4	$29.94	8.327%	$32.4331	$32.43	$32.45	$32.40
Purchase #5	$40.58	7.597%	$43.6629	$43.66	$43.65	$43.70
Purchase #6	$9.66	6.297%	$10.2683	$10.27	$10.25	$10.30
Purchase #7	$165.95	12.406%	$186.5378	$186.54	$186.55	$186.50
7 purchase totals =	$527.03		$580.2794	$580.28	$580.30	$580.30