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	$117.98	12.197%	$132.37	$132.37	$132.35	$132.40
Purchase #2	$200.77	4.348%	$209.4995	$209.50	$209.50	$209.50
Purchase #3	$18.79	6.419%	$19.9961	$20.00	$20.00	$20.00
Purchase #4	$242.77	5.419%	$255.9257	$255.93	$255.95	$255.90
Purchase #5	$132.27	13.563%	$150.2098	$150.21	$150.20	$150.20
Purchase #6	$137.40	10.501%	$151.8284	$151.83	$151.85	$151.80
Purchase #7	$16.55	13.161%	$18.7281	$18.73	$18.75	$18.70
7 purchase totals =	$866.53		$938.5576	$938.57	$938.60	$938.50