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	$45.44	8.222%	$49.1761	$49.18	$49.20	$49.20
Purchase #2	$81.40	11.329%	$90.6218	$90.62	$90.60	$90.60
Purchase #3	$12.27	12.521%	$13.8063	$13.81	$13.80	$13.80
Purchase #4	$238.52	11.140%	$265.0911	$265.09	$265.10	$265.10
Purchase #5	$234.64	13.308%	$265.8659	$265.87	$265.85	$265.90
Purchase #6	$183.29	4.181%	$190.9534	$190.95	$190.95	$191.00
Purchase #7	$12.63	13.274%	$14.3065	$14.31	$14.30	$14.30
7 purchase totals =	$808.19		$889.8211	$889.83	$889.80	$889.90