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	$105.98	11.463%	$118.1285	$118.13	$118.15	$118.10
Purchase #2	$225.52	13.112%	$255.0902	$255.09	$255.10	$255.10
Purchase #3	$140.42	10.587%	$155.2863	$155.29	$155.30	$155.30
Purchase #4	$230.39	12.403%	$258.9653	$258.97	$258.95	$259.00
Purchase #5	$37.56	6.313%	$39.9312	$39.93	$39.95	$39.90
Purchase #6	$191.29	12.660%	$215.5073	$215.51	$215.50	$215.50
Purchase #7	$41.90	6.792%	$44.7458	$44.75	$44.75	$44.70
7 purchase totals =	$973.06		$1,087.6546	$1,087.67	$1,087.70	$1,087.60