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	$59.81	10.613%	$66.1576	$66.16	$66.15	$66.20
Purchase #2	$226.89	11.518%	$253.0232	$253.02	$253.00	$253.00
Purchase #3	$227.56	12.654%	$256.3554	$256.36	$256.35	$256.40
Purchase #4	$63.97	4.708%	$66.9817	$66.98	$67.00	$67.00
Purchase #5	$169.45	3.462%	$175.3164	$175.32	$175.30	$175.30
Purchase #6	$233.89	8.388%	$253.5087	$253.51	$253.50	$253.50
Purchase #7	$190.62	13.799%	$216.9237	$216.92	$216.90	$216.90
7 purchase totals =	$1,172.19		$1,288.2667	$1,288.27	$1,288.20	$1,288.30