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	$157.96	13.249%	$178.8881	$178.89	$178.90	$178.90
Purchase #2	$44.76	12.601%	$50.4002	$50.40	$50.40	$50.40
Purchase #3	$24.60	3.521%	$25.4662	$25.47	$25.45	$25.50
Purchase #4	$80.71	7.493%	$86.7576	$86.76	$86.75	$86.80
Purchase #5	$78.93	11.834%	$88.2706	$88.27	$88.25	$88.30
Purchase #6	$56.50	4.594%	$59.0956	$59.10	$59.10	$59.10
Purchase #7	$170.94	11.619%	$190.8015	$190.80	$190.80	$190.80
7 purchase totals =	$614.40		$679.6798	$679.69	$679.65	$679.80