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	$99.56	12.461%	$111.9662	$111.97	$111.95	$112.00
Purchase #2	$7.45	5.510%	$7.8605	$7.86	$7.85	$7.90
Purchase #3	$103.93	12.258%	$116.6697	$116.67	$116.65	$116.70
Purchase #4	$204.30	5.300%	$215.1279	$215.13	$215.15	$215.10
Purchase #5	$38.52	10.742%	$42.6578	$42.66	$42.65	$42.70
Purchase #6	$188.66	13.794%	$214.6838	$214.68	$214.70	$214.70
Purchase #7	$125.76	9.486%	$137.6896	$137.69	$137.70	$137.70
7 purchase totals =	$768.18		$846.6555	$846.66	$846.65	$846.80