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	$151.30	4.488%	$158.0903	$158.09	$158.10	$158.10
Purchase #2	$214.55	5.224%	$225.7581	$225.76	$225.75	$225.80
Purchase #3	$125.72	8.509%	$136.4175	$136.42	$136.40	$136.40
Purchase #4	$139.55	10.415%	$154.0841	$154.08	$154.10	$154.10
Purchase #5	$107.71	4.741%	$112.8165	$112.82	$112.80	$112.80
Purchase #6	$30.99	5.241%	$32.6142	$32.61	$32.60	$32.60
Purchase #7	$249.66	12.218%	$280.1635	$280.16	$280.15	$280.20
7 purchase totals =	$1,019.48		$1,099.9442	$1,099.94	$1,099.90	$1,100.00