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	$237.66	8.523%	$257.9158	$257.92	$257.90	$257.90
Purchase #2	$49.39	5.816%	$52.2625	$52.26	$52.25	$52.30
Purchase #3	$241.96	9.559%	$265.089	$265.09	$265.10	$265.10
Purchase #4	$81.83	9.392%	$89.5155	$89.52	$89.50	$89.50
Purchase #5	$63.94	3.767%	$66.3486	$66.35	$66.35	$66.30
Purchase #6	$14.83	10.522%	$16.3904	$16.39	$16.40	$16.40
Purchase #7	$152.28	10.162%	$167.7547	$167.75	$167.75	$167.80
7 purchase totals =	$841.89		$915.2765	$915.28	$915.25	$915.30