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	$116.81	13.267%	$132.3072	$132.31	$132.30	$132.30
Purchase #2	$225.86	12.145%	$253.2907	$253.29	$253.30	$253.30
Purchase #3	$143.86	8.106%	$155.5213	$155.52	$155.50	$155.50
Purchase #4	$61.36	7.328%	$65.8565	$65.86	$65.85	$65.90
Purchase #5	$141.33	10.258%	$155.8276	$155.83	$155.85	$155.80
Purchase #6	$238.49	10.433%	$263.3717	$263.37	$263.35	$263.40
Purchase #7	$102.30	9.200%	$111.7116	$111.71	$111.70	$111.70
7 purchase totals =	$1,030.01		$1,137.8866	$1,137.89	$1,137.85	$1,137.90