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	$40.78	3.868%	$42.3574	$42.36	$42.35	$42.40
Purchase #2	$241.27	4.126%	$251.2248	$251.22	$251.20	$251.20
Purchase #3	$177.35	7.604%	$190.8357	$190.84	$190.85	$190.80
Purchase #4	$124.65	11.566%	$139.067	$139.07	$139.05	$139.10
Purchase #5	$185.57	13.587%	$210.7834	$210.78	$210.80	$210.80
Purchase #6	$72.64	8.255%	$78.6364	$78.64	$78.65	$78.60
Purchase #7	$166.30	10.610%	$183.9444	$183.94	$183.95	$183.90
7 purchase totals =	$1,008.56		$1,096.8491	$1,096.85	$1,096.85	$1,096.80