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	$38.92	8.594%	$42.2648	$42.26	$42.25	$42.30
Purchase #2	$20.83	9.128%	$22.7314	$22.73	$22.75	$22.70
Purchase #3	$151.97	9.526%	$166.4467	$166.45	$166.45	$166.40
Purchase #4	$56.41	5.589%	$59.5628	$59.56	$59.55	$59.60
Purchase #5	$237.69	6.698%	$253.6105	$253.61	$253.60	$253.60
Purchase #6	$7.60	5.471%	$8.0158	$8.02	$8.00	$8.00
Purchase #7	$131.81	9.205%	$143.9431	$143.94	$143.95	$143.90
7 purchase totals =	$645.23		$696.5751	$696.57	$696.55	$696.50