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	$9.59	9.157%	$10.4682	$10.47	$10.45	$10.50
Purchase #2	$40.30	13.152%	$45.6003	$45.60	$45.60	$45.60
Purchase #3	$112.76	3.743%	$116.9806	$116.98	$117.00	$117.00
Purchase #4	$195.96	13.299%	$222.0207	$222.02	$222.00	$222.00
Purchase #5	$39.34	13.293%	$44.5695	$44.57	$44.55	$44.60
Purchase #6	$52.46	7.708%	$56.5036	$56.50	$56.50	$56.50
Purchase #7	$29.53	7.426%	$31.7229	$31.72	$31.70	$31.70
7 purchase totals =	$479.94		$527.8658	$527.86	$527.80	$527.90