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	$158.45	7.833%	$170.8614	$170.86	$170.85	$170.90
Purchase #2	$137.28	12.502%	$154.4427	$154.44	$154.45	$154.40
Purchase #3	$49.83	8.771%	$54.2006	$54.20	$54.20	$54.20
Purchase #4	$217.89	4.687%	$228.1025	$228.10	$228.10	$228.10
Purchase #5	$138.88	4.149%	$144.6421	$144.64	$144.65	$144.60
Purchase #6	$119.40	10.624%	$132.0851	$132.09	$132.10	$132.10
Purchase #7	$68.83	13.446%	$78.0849	$78.08	$78.10	$78.10
7 purchase totals =	$890.56		$962.4193	$962.41	$962.45	$962.40