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	$117.86	12.855%	$133.0109	$133.01	$133.00	$133.00
Purchase #2	$90.73	8.692%	$98.6163	$98.62	$98.60	$98.60
Purchase #3	$128.95	12.787%	$145.4388	$145.44	$145.45	$145.40
Purchase #4	$99.95	11.718%	$111.6621	$111.66	$111.65	$111.70
Purchase #5	$233.45	9.581%	$255.8168	$255.82	$255.80	$255.80
Purchase #6	$99.66	5.806%	$105.4463	$105.45	$105.45	$105.40
Purchase #7	$43.39	10.716%	$48.0397	$48.04	$48.05	$48.00
7 purchase totals =	$813.99		$898.0309	$898.04	$898.00	$897.90