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	$60.37	10.772%	$66.8731	$66.87	$66.85	$66.90
Purchase #2	$111.40	4.630%	$116.5578	$116.56	$116.55	$116.60
Purchase #3	$238.79	10.659%	$264.2426	$264.24	$264.25	$264.20
Purchase #4	$171.39	3.562%	$177.4949	$177.49	$177.50	$177.50
Purchase #5	$243.94	7.720%	$262.7722	$262.77	$262.75	$262.80
Purchase #6	$134.80	12.525%	$151.6837	$151.68	$151.70	$151.70
Purchase #7	$117.60	8.174%	$127.2126	$127.21	$127.20	$127.20
7 purchase totals =	$1,078.29		$1,166.8369	$1,166.82	$1,166.80	$1,166.90