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	$151.97	4.289%	$158.488	$158.49	$158.50	$158.50
Purchase #2	$163.43	9.410%	$178.8088	$178.81	$178.80	$178.80
Purchase #3	$215.72	10.846%	$239.117	$239.12	$239.10	$239.10
Purchase #4	$37.26	9.279%	$40.7174	$40.72	$40.70	$40.70
Purchase #5	$6.99	4.230%	$7.2857	$7.29	$7.30	$7.30
Purchase #6	$173.81	10.190%	$191.5212	$191.52	$191.50	$191.50
Purchase #7	$52.48	7.827%	$56.5876	$56.59	$56.60	$56.60
7 purchase totals =	$801.66		$872.5257	$872.54	$872.50	$872.50