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	$39.70	3.491%	$41.0859	$41.09	$41.10	$41.10
Purchase #2	$205.35	8.189%	$222.1661	$222.17	$222.15	$222.20
Purchase #3	$27.74	5.571%	$29.2854	$29.29	$29.30	$29.30
Purchase #4	$197.64	9.269%	$215.9593	$215.96	$215.95	$216.00
Purchase #5	$78.78	4.653%	$82.4456	$82.45	$82.45	$82.40
Purchase #6	$42.90	9.298%	$46.8888	$46.89	$46.90	$46.90
Purchase #7	$230.66	10.613%	$255.1399	$255.14	$255.15	$255.10
7 purchase totals =	$822.77		$892.9710	$892.99	$893.00	$893.00