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	$62.53	9.577%	$68.5185	$68.52	$68.50	$68.50
Purchase #2	$94.29	6.136%	$100.0756	$100.08	$100.10	$100.10
Purchase #3	$11.88	9.686%	$13.0307	$13.03	$13.05	$13.00
Purchase #4	$248.69	12.565%	$279.9379	$279.94	$279.95	$279.90
Purchase #5	$104.25	5.251%	$109.7242	$109.72	$109.70	$109.70
Purchase #6	$184.52	3.215%	$190.4523	$190.45	$190.45	$190.50
Purchase #7	$180.41	5.836%	$190.9387	$190.94	$190.95	$190.90
7 purchase totals =	$886.57		$952.6779	$952.68	$952.70	$952.60