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	$9.40	11.303%	$10.4625	$10.46	$10.45	$10.50
Purchase #2	$131.76	5.774%	$139.3678	$139.37	$139.35	$139.40
Purchase #3	$78.66	3.504%	$81.4162	$81.42	$81.40	$81.40
Purchase #4	$128.98	12.291%	$144.8329	$144.83	$144.85	$144.80
Purchase #5	$17.66	4.644%	$18.4801	$18.48	$18.50	$18.50
Purchase #6	$189.82	5.756%	$200.746	$200.75	$200.75	$200.70
Purchase #7	$157.47	10.555%	$174.091	$174.09	$174.10	$174.10
7 purchase totals =	$713.75		$769.3965	$769.40	$769.40	$769.40