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	$14.35	8.213%	$15.5286	$15.53	$15.55	$15.50
Purchase #2	$99.95	11.610%	$111.5542	$111.55	$111.55	$111.60
Purchase #3	$222.38	12.301%	$249.735	$249.74	$249.75	$249.70
Purchase #4	$48.69	9.159%	$53.1495	$53.15	$53.15	$53.10
Purchase #5	$226.95	8.568%	$246.3951	$246.40	$246.40	$246.40
Purchase #6	$144.69	3.385%	$149.5878	$149.59	$149.60	$149.60
Purchase #7	$158.31	4.537%	$165.4925	$165.49	$165.50	$165.50
7 purchase totals =	$915.32		$991.4427	$991.45	$991.50	$991.40