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	$190.76	7.791%	$205.6221	$205.62	$205.60	$205.60
Purchase #2	$131.67	10.527%	$145.5309	$145.53	$145.55	$145.50
Purchase #3	$105.96	5.255%	$111.5282	$111.53	$111.55	$111.50
Purchase #4	$77.26	6.166%	$82.0239	$82.02	$82.00	$82.00
Purchase #5	$150.68	4.832%	$157.9609	$157.96	$157.95	$158.00
Purchase #6	$247.53	12.312%	$278.0059	$278.01	$278.00	$278.00
Purchase #7	$183.29	13.600%	$208.2174	$208.22	$208.20	$208.20
7 purchase totals =	$1,087.15		$1,188.8893	$1,188.89	$1,188.85	$1,188.80