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	$39.95	4.142%	$41.6047	$41.60	$41.60	$41.60
Purchase #2	$76.53	11.573%	$85.3868	$85.39	$85.40	$85.40
Purchase #3	$151.77	8.779%	$165.0939	$165.09	$165.10	$165.10
Purchase #4	$130.82	10.137%	$144.0812	$144.08	$144.10	$144.10
Purchase #5	$69.66	9.750%	$76.4519	$76.45	$76.45	$76.50
Purchase #6	$238.32	6.388%	$253.5439	$253.54	$253.55	$253.50
Purchase #7	$56.98	12.789%	$64.2672	$64.27	$64.25	$64.30
7 purchase totals =	$764.03		$830.4296	$830.42	$830.45	$830.50