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	$42.89	6.391%	$45.6311	$45.63	$45.65	$45.60
Purchase #2	$142.61	5.485%	$150.4322	$150.43	$150.45	$150.40
Purchase #3	$20.50	5.737%	$21.6761	$21.68	$21.70	$21.70
Purchase #4	$137.84	9.225%	$150.5557	$150.56	$150.55	$150.60
Purchase #5	$103.99	9.483%	$113.8514	$113.85	$113.85	$113.90
Purchase #6	$213.80	4.792%	$224.0453	$224.05	$224.05	$224.00
Purchase #7	$143.77	11.387%	$160.1411	$160.14	$160.15	$160.10
7 purchase totals =	$805.40		$866.3329	$866.34	$866.40	$866.30