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	$155.98	10.516%	$172.3829	$172.38	$172.40	$172.40
Purchase #2	$248.25	12.733%	$279.8597	$279.86	$279.85	$279.90
Purchase #3	$176.71	7.601%	$190.1417	$190.14	$190.15	$190.10
Purchase #4	$235.85	9.682%	$258.685	$258.69	$258.70	$258.70
Purchase #5	$78.96	11.395%	$87.9575	$87.96	$87.95	$88.00
Purchase #6	$200.50	11.874%	$224.3074	$224.31	$224.30	$224.30
Purchase #7	$123.88	12.701%	$139.614	$139.61	$139.60	$139.60
7 purchase totals =	$1,220.13		$1,352.9482	$1,352.95	$1,352.95	$1,353.00