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	$152.38	8.539%	$165.3917	$165.39	$165.40	$165.40
Purchase #2	$250.75	11.863%	$280.4965	$280.50	$280.50	$280.50
Purchase #3	$162.49	5.534%	$171.4822	$171.48	$171.50	$171.50
Purchase #4	$172.83	4.509%	$180.6229	$180.62	$180.60	$180.60
Purchase #5	$44.53	11.153%	$49.4964	$49.50	$49.50	$49.50
Purchase #6	$10.88	12.137%	$12.2005	$12.20	$12.20	$12.20
Purchase #7	$72.46	3.116%	$74.7179	$74.72	$74.70	$74.70
7 purchase totals =	$866.32		$934.4081	$934.41	$934.40	$934.40