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	$241.56	12.845%	$272.5884	$272.59	$272.60	$272.60
Purchase #2	$184.82	3.123%	$190.5919	$190.59	$190.60	$190.60
Purchase #3	$226.73	13.188%	$256.6312	$256.63	$256.65	$256.60
Purchase #4	$150.97	9.631%	$165.5099	$165.51	$165.50	$165.50
Purchase #5	$53.60	6.128%	$56.8846	$56.88	$56.90	$56.90
Purchase #6	$221.93	8.456%	$240.6964	$240.70	$240.70	$240.70
Purchase #7	$233.54	10.161%	$257.27	$257.27	$257.25	$257.30
7 purchase totals =	$1,313.15		$1,440.1724	$1,440.17	$1,440.20	$1,440.20