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	$51.27	6.291%	$54.4954	$54.50	$54.50	$54.50
Purchase #2	$36.54	6.514%	$38.9202	$38.92	$38.90	$38.90
Purchase #3	$41.77	13.771%	$47.5221	$47.52	$47.50	$47.50
Purchase #4	$143.89	11.729%	$160.7669	$160.77	$160.75	$160.80
Purchase #5	$234.94	13.683%	$267.0868	$267.09	$267.10	$267.10
Purchase #6	$244.98	8.821%	$266.5897	$266.59	$266.60	$266.60
Purchase #7	$176.39	7.774%	$190.1026	$190.10	$190.10	$190.10
7 purchase totals =	$929.78		$1,025.4837	$1,025.49	$1,025.45	$1,025.50