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	$11.99	9.285%	$13.1033	$13.10	$13.10	$13.10
Purchase #2	$139.90	7.603%	$150.5366	$150.54	$150.55	$150.50
Purchase #3	$169.37	13.585%	$192.3789	$192.38	$192.40	$192.40
Purchase #4	$105.54	8.272%	$114.2703	$114.27	$114.25	$114.30
Purchase #5	$195.83	9.584%	$214.5983	$214.60	$214.60	$214.60
Purchase #6	$100.27	5.223%	$105.5071	$105.51	$105.50	$105.50
Purchase #7	$90.58	11.186%	$100.7123	$100.71	$100.70	$100.70
7 purchase totals =	$813.48		$891.1068	$891.11	$891.10	$891.10