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	$37.76	4.692%	$39.5317	$39.53	$39.55	$39.50
Purchase #2	$52.30	6.644%	$55.7748	$55.77	$55.75	$55.80
Purchase #3	$128.82	11.365%	$143.4604	$143.46	$143.45	$143.50
Purchase #4	$129.48	10.546%	$143.135	$143.14	$143.15	$143.10
Purchase #5	$114.51	5.337%	$120.6214	$120.62	$120.60	$120.60
Purchase #6	$109.69	10.212%	$120.8915	$120.89	$120.90	$120.90
Purchase #7	$234.42	5.561%	$247.4561	$247.46	$247.45	$247.50
7 purchase totals =	$806.98		$870.8709	$870.87	$870.85	$870.90