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	$228.30	10.754%	$252.8514	$252.85	$252.85	$252.90
Purchase #2	$80.30	6.196%	$85.2754	$85.28	$85.30	$85.30
Purchase #3	$134.70	7.584%	$144.9156	$144.92	$144.90	$144.90
Purchase #4	$175.32	13.690%	$199.3213	$199.32	$199.30	$199.30
Purchase #5	$99.74	8.795%	$108.5121	$108.51	$108.50	$108.50
Purchase #6	$37.48	5.134%	$39.4042	$39.40	$39.40	$39.40
Purchase #7	$128.72	6.106%	$136.5796	$136.58	$136.60	$136.60
7 purchase totals =	$884.56		$966.8596	$966.86	$966.85	$966.90