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	$177.95	12.143%	$199.5585	$199.56	$199.55	$199.60
Purchase #2	$205.54	11.784%	$229.7608	$229.76	$229.75	$229.80
Purchase #3	$11.98	12.765%	$13.5092	$13.51	$13.50	$13.50
Purchase #4	$18.54	12.610%	$20.8779	$20.88	$20.90	$20.90
Purchase #5	$100.28	11.518%	$111.8303	$111.83	$111.85	$111.80
Purchase #6	$40.67	9.751%	$44.6357	$44.64	$44.65	$44.60
Purchase #7	$21.99	4.838%	$23.0539	$23.05	$23.05	$23.10
7 purchase totals =	$576.95		$643.2263	$643.23	$643.25	$643.30