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	$24.89	12.661%	$28.0413	$28.04	$28.05	$28.00
Purchase #2	$143.60	12.248%	$161.1881	$161.19	$161.20	$161.20
Purchase #3	$232.94	13.822%	$265.137	$265.14	$265.15	$265.10
Purchase #4	$79.89	13.256%	$90.4802	$90.48	$90.50	$90.50
Purchase #5	$58.64	12.246%	$65.8211	$65.82	$65.80	$65.80
Purchase #6	$199.57	3.495%	$206.545	$206.55	$206.55	$206.50
Purchase #7	$9.33	13.725%	$10.6105	$10.61	$10.60	$10.60
7 purchase totals =	$748.86		$827.8232	$827.83	$827.85	$827.70