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	$51.87	11.374%	$57.7697	$57.77	$57.75	$57.80
Purchase #2	$182.59	3.766%	$189.4663	$189.47	$189.45	$189.50
Purchase #3	$124.72	11.823%	$139.4656	$139.47	$139.45	$139.50
Purchase #4	$112.50	3.808%	$116.784	$116.78	$116.80	$116.80
Purchase #5	$31.72	9.324%	$34.6776	$34.68	$34.70	$34.70
Purchase #6	$146.45	5.686%	$154.7771	$154.78	$154.80	$154.80
Purchase #7	$106.86	6.774%	$114.0987	$114.10	$114.10	$114.10
7 purchase totals =	$756.71		$807.0390	$807.05	$807.05	$807.20