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	$144.51	9.573%	$158.3439	$158.34	$158.35	$158.30
Purchase #2	$34.52	13.450%	$39.1629	$39.16	$39.15	$39.20
Purchase #3	$29.63	7.439%	$31.8342	$31.83	$31.85	$31.80
Purchase #4	$24.78	10.804%	$27.4572	$27.46	$27.45	$27.50
Purchase #5	$132.65	13.563%	$150.6413	$150.64	$150.65	$150.60
Purchase #6	$231.60	10.793%	$256.5966	$256.60	$256.60	$256.60
Purchase #7	$217.83	3.230%	$224.8659	$224.87	$224.85	$224.90
7 purchase totals =	$815.52		$888.9020	$888.90	$888.90	$888.90