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	$250.90	3.294%	$259.1646	$259.16	$259.15	$259.20
Purchase #2	$178.97	5.215%	$188.3033	$188.30	$188.30	$188.30
Purchase #3	$50.83	7.768%	$54.7785	$54.78	$54.80	$54.80
Purchase #4	$183.46	11.105%	$203.8332	$203.83	$203.85	$203.80
Purchase #5	$160.90	8.159%	$174.0278	$174.03	$174.05	$174.00
Purchase #6	$107.94	7.734%	$116.2881	$116.29	$116.30	$116.30
Purchase #7	$155.85	13.179%	$176.3895	$176.39	$176.40	$176.40
7 purchase totals =	$1,088.85		$1,172.7850	$1,172.78	$1,172.85	$1,172.80