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	$156.33	10.644%	$172.9698	$172.97	$172.95	$173.00
Purchase #2	$27.99	6.257%	$29.7413	$29.74	$29.75	$29.70
Purchase #3	$101.87	3.721%	$105.6606	$105.66	$105.65	$105.70
Purchase #4	$118.82	13.489%	$134.8476	$134.85	$134.85	$134.80
Purchase #5	$14.89	4.368%	$15.5404	$15.54	$15.55	$15.50
Purchase #6	$100.93	10.489%	$111.5165	$111.52	$111.50	$111.50
Purchase #7	$17.58	8.604%	$19.0926	$19.09	$19.10	$19.10
7 purchase totals =	$538.41		$589.3688	$589.37	$589.35	$589.30