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	$140.83	10.694%	$155.8904	$155.89	$155.90	$155.90
Purchase #2	$205.27	8.281%	$222.2684	$222.27	$222.25	$222.30
Purchase #3	$136.91	7.755%	$147.5274	$147.53	$147.55	$147.50
Purchase #4	$185.94	10.710%	$205.8542	$205.85	$205.85	$205.90
Purchase #5	$44.99	12.645%	$50.679	$50.68	$50.70	$50.70
Purchase #6	$13.72	6.573%	$14.6218	$14.62	$14.60	$14.60
Purchase #7	$151.27	5.509%	$159.6035	$159.60	$159.60	$159.60
7 purchase totals =	$878.93		$956.4447	$956.44	$956.45	$956.50