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	$32.64	3.311%	$33.7207	$33.72	$33.70	$33.70
Purchase #2	$100.99	10.321%	$111.4132	$111.41	$111.40	$111.40
Purchase #3	$100.84	11.799%	$112.7381	$112.74	$112.75	$112.70
Purchase #4	$149.40	13.182%	$169.0939	$169.09	$169.10	$169.10
Purchase #5	$60.49	3.631%	$62.6864	$62.69	$62.70	$62.70
Purchase #6	$46.86	9.789%	$51.4471	$51.45	$51.45	$51.40
Purchase #7	$79.69	10.302%	$87.8997	$87.90	$87.90	$87.90
7 purchase totals =	$570.91		$628.9991	$629.00	$629.00	$628.90