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	$111.51	5.813%	$117.9921	$117.99	$118.00	$118.00
Purchase #2	$164.95	3.575%	$170.847	$170.85	$170.85	$170.80
Purchase #3	$123.58	13.667%	$140.4697	$140.47	$140.45	$140.50
Purchase #4	$100.39	8.670%	$109.0938	$109.09	$109.10	$109.10
Purchase #5	$229.67	12.563%	$258.5234	$258.52	$258.50	$258.50
Purchase #6	$240.97	4.357%	$251.4691	$251.47	$251.45	$251.50
Purchase #7	$80.70	12.707%	$90.9545	$90.95	$90.95	$91.00
7 purchase totals =	$1,051.77		$1,139.3496	$1,139.34	$1,139.30	$1,139.40