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	$142.72	8.304%	$154.5715	$154.57	$154.55	$154.60
Purchase #2	$151.89	11.729%	$169.7052	$169.71	$169.70	$169.70
Purchase #3	$231.40	10.495%	$255.6854	$255.69	$255.70	$255.70
Purchase #4	$54.34	9.184%	$59.3306	$59.33	$59.35	$59.30
Purchase #5	$219.97	5.244%	$231.5052	$231.51	$231.50	$231.50
Purchase #6	$33.64	8.426%	$36.4745	$36.47	$36.45	$36.50
Purchase #7	$91.42	9.580%	$100.178	$100.18	$100.20	$100.20
7 purchase totals =	$925.38		$1,007.4504	$1,007.46	$1,007.45	$1,007.50