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	$112.73	13.437%	$127.8775	$127.88	$127.90	$127.90
Purchase #2	$101.49	4.288%	$105.8419	$105.84	$105.85	$105.80
Purchase #3	$49.68	6.855%	$53.0856	$53.09	$53.10	$53.10
Purchase #4	$113.83	12.692%	$128.2773	$128.28	$128.30	$128.30
Purchase #5	$24.69	7.387%	$26.5139	$26.51	$26.50	$26.50
Purchase #6	$31.44	9.611%	$34.4617	$34.46	$34.45	$34.50
Purchase #7	$135.85	9.546%	$148.8182	$148.82	$148.80	$148.80
7 purchase totals =	$569.71		$624.8761	$624.88	$624.90	$624.90