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	$56.60	11.556%	$63.1407	$63.14	$63.15	$63.10
Purchase #2	$171.35	11.181%	$190.5086	$190.51	$190.50	$190.50
Purchase #3	$11.50	9.168%	$12.5543	$12.55	$12.55	$12.60
Purchase #4	$153.39	11.625%	$171.2216	$171.22	$171.20	$171.20
Purchase #5	$151.92	4.623%	$158.9433	$158.94	$158.95	$158.90
Purchase #6	$239.25	12.782%	$269.8309	$269.83	$269.85	$269.80
Purchase #7	$111.32	12.128%	$124.8209	$124.82	$124.80	$124.80
7 purchase totals =	$895.33		$991.0203	$991.01	$991.00	$990.90