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	$157.64	13.297%	$178.6014	$178.60	$178.60	$178.60
Purchase #2	$140.77	7.191%	$150.8928	$150.89	$150.90	$150.90
Purchase #3	$110.50	5.409%	$116.4769	$116.48	$116.50	$116.50
Purchase #4	$127.70	4.281%	$133.1668	$133.17	$133.15	$133.20
Purchase #5	$111.40	5.451%	$117.4724	$117.47	$117.45	$117.50
Purchase #6	$177.55	7.491%	$190.8503	$190.85	$190.85	$190.90
Purchase #7	$239.84	7.803%	$258.5547	$258.55	$258.55	$258.60
7 purchase totals =	$1,065.40		$1,146.0153	$1,146.01	$1,146.00	$1,146.20