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	$99.34	8.632%	$107.915	$107.92	$107.90	$107.90
Purchase #2	$84.70	6.348%	$90.0768	$90.08	$90.10	$90.10
Purchase #3	$11.77	13.674%	$13.3794	$13.38	$13.40	$13.40
Purchase #4	$20.52	5.201%	$21.5872	$21.59	$21.60	$21.60
Purchase #5	$34.89	13.187%	$39.4909	$39.49	$39.50	$39.50
Purchase #6	$208.72	7.521%	$224.4178	$224.42	$224.40	$224.40
Purchase #7	$74.85	11.526%	$83.4772	$83.48	$83.50	$83.50
7 purchase totals =	$534.79		$580.3443	$580.36	$580.40	$580.40