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	$135.40	11.650%	$151.1741	$151.17	$151.15	$151.20
Purchase #2	$95.59	11.356%	$106.4452	$106.45	$106.45	$106.40
Purchase #3	$9.60	12.774%	$10.8263	$10.83	$10.85	$10.80
Purchase #4	$71.58	9.462%	$78.3529	$78.35	$78.35	$78.40
Purchase #5	$190.50	11.311%	$212.0475	$212.05	$212.05	$212.00
Purchase #6	$12.97	6.505%	$13.8137	$13.81	$13.80	$13.80
Purchase #7	$19.69	9.406%	$21.542	$21.54	$21.55	$21.50
7 purchase totals =	$535.33		$594.2017	$594.20	$594.20	$594.10