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	$7.96	11.308%	$8.8601	$8.86	$8.85	$8.90
Purchase #2	$103.29	12.700%	$116.4078	$116.41	$116.40	$116.40
Purchase #3	$22.48	13.136%	$25.433	$25.43	$25.45	$25.40
Purchase #4	$169.65	5.414%	$178.8349	$178.83	$178.85	$178.80
Purchase #5	$59.62	11.551%	$66.5067	$66.51	$66.50	$66.50
Purchase #6	$81.28	4.242%	$84.7279	$84.73	$84.75	$84.70
Purchase #7	$85.75	5.641%	$90.5872	$90.59	$90.60	$90.60
7 purchase totals =	$530.03		$571.3576	$571.36	$571.40	$571.30