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	$75.61	11.534%	$84.3309	$84.33	$84.35	$84.30
Purchase #2	$82.90	9.495%	$90.7714	$90.77	$90.75	$90.80
Purchase #3	$41.76	13.485%	$47.3913	$47.39	$47.40	$47.40
Purchase #4	$57.98	13.104%	$65.5777	$65.58	$65.60	$65.60
Purchase #5	$187.87	6.760%	$200.57	$200.57	$200.55	$200.60
Purchase #6	$51.27	10.104%	$56.4503	$56.45	$56.45	$56.50
Purchase #7	$176.85	7.422%	$189.9758	$189.98	$190.00	$190.00
7 purchase totals =	$674.24		$735.0674	$735.07	$735.10	$735.20