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	$10.69	8.243%	$11.5712	$11.57	$11.55	$11.60
Purchase #2	$126.37	5.611%	$133.4606	$133.46	$133.45	$133.50
Purchase #3	$47.49	5.353%	$50.0321	$50.03	$50.05	$50.00
Purchase #4	$183.88	11.335%	$204.7228	$204.72	$204.70	$204.70
Purchase #5	$152.61	5.213%	$160.5656	$160.57	$160.55	$160.60
Purchase #6	$123.72	6.675%	$131.9783	$131.98	$132.00	$132.00
Purchase #7	$141.60	7.714%	$152.523	$152.52	$152.50	$152.50
7 purchase totals =	$786.36		$844.8536	$844.85	$844.80	$844.90