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	$12.66	4.624%	$13.2454	$13.25	$13.25	$13.20
Purchase #2	$244.87	13.229%	$277.2639	$277.26	$277.25	$277.30
Purchase #3	$129.60	7.702%	$139.5818	$139.58	$139.60	$139.60
Purchase #4	$43.86	9.615%	$48.0771	$48.08	$48.10	$48.10
Purchase #5	$248.95	5.401%	$262.3958	$262.40	$262.40	$262.40
Purchase #6	$100.72	4.646%	$105.3995	$105.40	$105.40	$105.40
Purchase #7	$43.79	6.150%	$46.4831	$46.48	$46.50	$46.50
7 purchase totals =	$824.45		$892.4466	$892.45	$892.50	$892.50