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	$240.86	6.495%	$256.5039	$256.50	$256.50	$256.50
Purchase #2	$122.83	12.108%	$137.7023	$137.70	$137.70	$137.70
Purchase #3	$248.89	12.861%	$280.8997	$280.90	$280.90	$280.90
Purchase #4	$148.39	5.207%	$156.1167	$156.12	$156.10	$156.10
Purchase #5	$117.53	10.529%	$129.9047	$129.90	$129.90	$129.90
Purchase #6	$168.71	11.357%	$187.8704	$187.87	$187.85	$187.90
Purchase #7	$148.79	6.620%	$158.6399	$158.64	$158.65	$158.60
7 purchase totals =	$1,196.00		$1,307.6376	$1,307.63	$1,307.60	$1,307.60