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	$216.61	12.585%	$243.8704	$243.87	$243.85	$243.90
Purchase #2	$122.47	12.392%	$137.6465	$137.65	$137.65	$137.60
Purchase #3	$57.90	13.594%	$65.7709	$65.77	$65.75	$65.80
Purchase #4	$59.94	10.447%	$66.2019	$66.20	$66.20	$66.20
Purchase #5	$175.84	8.509%	$190.8022	$190.80	$190.80	$190.80
Purchase #6	$90.53	10.578%	$100.1063	$100.11	$100.10	$100.10
Purchase #7	$105.52	10.441%	$116.5373	$116.54	$116.55	$116.50
7 purchase totals =	$828.81		$920.9355	$920.94	$920.90	$920.90