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	$12.57	5.128%	$13.2146	$13.21	$13.20	$13.20
Purchase #2	$100.80	4.779%	$105.6172	$105.62	$105.60	$105.60
Purchase #3	$171.28	11.271%	$190.585	$190.59	$190.60	$190.60
Purchase #4	$120.76	11.390%	$134.5146	$134.51	$134.50	$134.50
Purchase #5	$160.98	12.762%	$181.5243	$181.52	$181.50	$181.50
Purchase #6	$94.58	9.333%	$103.4072	$103.41	$103.40	$103.40
Purchase #7	$27.27	6.665%	$29.0875	$29.09	$29.10	$29.10
7 purchase totals =	$688.24		$757.9504	$757.95	$757.90	$757.90