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	$10.45	13.780%	$11.89	$11.89	$11.90	$11.90
Purchase #2	$169.28	6.847%	$180.8706	$180.87	$180.85	$180.90
Purchase #3	$244.60	8.792%	$266.1052	$266.11	$266.10	$266.10
Purchase #4	$90.69	5.471%	$95.6516	$95.65	$95.65	$95.70
Purchase #5	$71.46	7.766%	$77.0096	$77.01	$77.00	$77.00
Purchase #6	$27.51	6.809%	$29.3832	$29.38	$29.40	$29.40
Purchase #7	$159.68	8.662%	$173.5115	$173.51	$173.50	$173.50
7 purchase totals =	$773.67		$834.4217	$834.42	$834.40	$834.50