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	$227.87	12.679%	$256.7616	$256.76	$256.75	$256.80
Purchase #2	$24.30	11.847%	$27.1788	$27.18	$27.20	$27.20
Purchase #3	$133.58	11.288%	$148.6585	$148.66	$148.65	$148.70
Purchase #4	$46.96	4.122%	$48.8957	$48.90	$48.90	$48.90
Purchase #5	$246.48	7.734%	$265.5428	$265.54	$265.55	$265.50
Purchase #6	$71.82	9.803%	$78.8605	$78.86	$78.85	$78.90
Purchase #7	$141.66	11.166%	$157.4778	$157.48	$157.50	$157.50
7 purchase totals =	$892.67		$983.3757	$983.38	$983.40	$983.50