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	$171.89	10.553%	$190.0296	$190.03	$190.05	$190.00
Purchase #2	$19.57	7.390%	$21.0162	$21.02	$21.00	$21.00
Purchase #3	$158.29	13.338%	$179.4027	$179.40	$179.40	$179.40
Purchase #4	$144.51	13.535%	$164.0694	$164.07	$164.05	$164.10
Purchase #5	$222.78	4.853%	$233.5915	$233.59	$233.60	$233.60
Purchase #6	$131.70	9.408%	$144.0903	$144.09	$144.10	$144.10
Purchase #7	$145.76	8.202%	$157.7152	$157.72	$157.70	$157.70
7 purchase totals =	$994.50		$1,089.9149	$1,089.92	$1,089.90	$1,089.90