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	$49.67	8.375%	$53.8299	$53.83	$53.85	$53.80
Purchase #2	$213.87	9.341%	$233.8476	$233.85	$233.85	$233.80
Purchase #3	$198.77	13.234%	$225.0752	$225.08	$225.10	$225.10
Purchase #4	$34.87	13.563%	$39.5994	$39.60	$39.60	$39.60
Purchase #5	$126.34	10.358%	$139.4263	$139.43	$139.45	$139.40
Purchase #6	$87.64	6.323%	$93.1815	$93.18	$93.20	$93.20
Purchase #7	$205.51	12.799%	$231.8132	$231.81	$231.80	$231.80
7 purchase totals =	$916.67		$1,016.7731	$1,016.78	$1,016.85	$1,016.70