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	$12.64	9.458%	$13.8355	$13.84	$13.85	$13.80
Purchase #2	$177.78	12.223%	$199.51	$199.51	$199.50	$199.50
Purchase #3	$95.55	7.398%	$102.6188	$102.62	$102.60	$102.60
Purchase #4	$100.46	8.745%	$109.2452	$109.25	$109.25	$109.20
Purchase #5	$223.91	10.128%	$246.5876	$246.59	$246.60	$246.60
Purchase #6	$82.67	8.291%	$89.5242	$89.52	$89.50	$89.50
Purchase #7	$44.96	8.586%	$48.8203	$48.82	$48.80	$48.80
7 purchase totals =	$737.97		$810.1416	$810.15	$810.10	$810.00