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	$71.91	13.329%	$81.4949	$81.49	$81.50	$81.50
Purchase #2	$228.64	9.269%	$249.8326	$249.83	$249.85	$249.80
Purchase #3	$90.53	11.425%	$100.8731	$100.87	$100.85	$100.90
Purchase #4	$101.47	4.715%	$106.2543	$106.25	$106.25	$106.30
Purchase #5	$220.44	7.320%	$236.5762	$236.58	$236.60	$236.60
Purchase #6	$129.81	10.575%	$143.5374	$143.54	$143.55	$143.50
Purchase #7	$48.78	3.479%	$50.4771	$50.48	$50.50	$50.50
7 purchase totals =	$891.58		$969.0456	$969.04	$969.10	$969.10