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	$48.86	6.301%	$51.9387	$51.94	$51.95	$51.90
Purchase #2	$135.87	6.456%	$144.6418	$144.64	$144.65	$144.60
Purchase #3	$52.32	10.189%	$57.6509	$57.65	$57.65	$57.70
Purchase #4	$102.54	11.741%	$114.5792	$114.58	$114.60	$114.60
Purchase #5	$89.89	11.538%	$100.2615	$100.26	$100.25	$100.30
Purchase #6	$238.71	9.841%	$262.2015	$262.20	$262.20	$262.20
Purchase #7	$68.71	5.623%	$72.5736	$72.57	$72.55	$72.60
7 purchase totals =	$736.90		$803.8472	$803.84	$803.85	$803.90