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	$13.44	8.801%	$14.6229	$14.62	$14.60	$14.60
Purchase #2	$151.91	13.622%	$172.6032	$172.60	$172.60	$172.60
Purchase #3	$83.38	6.150%	$88.5079	$88.51	$88.50	$88.50
Purchase #4	$60.36	10.616%	$66.7678	$66.77	$66.75	$66.80
Purchase #5	$140.97	3.228%	$145.5205	$145.52	$145.50	$145.50
Purchase #6	$85.61	10.235%	$94.3722	$94.37	$94.35	$94.40
Purchase #7	$6.55	12.452%	$7.3656	$7.37	$7.35	$7.40
7 purchase totals =	$542.22		$589.7601	$589.76	$589.65	$589.80