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	$153.40	3.549%	$158.8442	$158.84	$158.85	$158.80
Purchase #2	$210.87	9.626%	$231.1683	$231.17	$231.15	$231.20
Purchase #3	$119.90	9.792%	$131.6406	$131.64	$131.65	$131.60
Purchase #4	$56.61	4.356%	$59.0759	$59.08	$59.10	$59.10
Purchase #5	$102.90	5.776%	$108.8435	$108.84	$108.85	$108.80
Purchase #6	$129.79	8.314%	$140.5807	$140.58	$140.60	$140.60
Purchase #7	$132.55	8.191%	$143.4072	$143.41	$143.40	$143.40
7 purchase totals =	$906.02		$973.5604	$973.56	$973.60	$973.50