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	$56.46	5.398%	$59.5077	$59.51	$59.50	$59.50
Purchase #2	$142.26	11.282%	$158.3098	$158.31	$158.30	$158.30
Purchase #3	$157.27	8.794%	$171.1003	$171.10	$171.10	$171.10
Purchase #4	$172.34	10.430%	$190.3151	$190.32	$190.30	$190.30
Purchase #5	$17.67	13.196%	$20.0017	$20.00	$20.00	$20.00
Purchase #6	$30.47	12.244%	$34.2007	$34.20	$34.20	$34.20
Purchase #7	$121.90	13.364%	$138.1907	$138.19	$138.20	$138.20
7 purchase totals =	$698.37		$771.6260	$771.63	$771.60	$771.60