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	$178.71	6.631%	$190.5603	$190.56	$190.55	$190.60
Purchase #2	$115.75	9.283%	$126.4951	$126.50	$126.50	$126.50
Purchase #3	$146.97	8.659%	$159.6961	$159.70	$159.70	$159.70
Purchase #4	$159.67	5.374%	$168.2507	$168.25	$168.25	$168.30
Purchase #5	$99.99	11.545%	$111.5338	$111.53	$111.55	$111.50
Purchase #6	$139.46	4.322%	$145.4875	$145.49	$145.50	$145.50
Purchase #7	$92.57	3.112%	$95.4508	$95.45	$95.45	$95.50
7 purchase totals =	$933.12		$997.4743	$997.48	$997.50	$997.60