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	$17.27	8.350%	$18.712	$18.71	$18.70	$18.70
Purchase #2	$249.38	12.507%	$280.57	$280.57	$280.55	$280.60
Purchase #3	$131.45	5.182%	$138.2617	$138.26	$138.25	$138.30
Purchase #4	$206.75	13.584%	$234.8349	$234.83	$234.85	$234.80
Purchase #5	$150.83	10.661%	$166.91	$166.91	$166.90	$166.90
Purchase #6	$13.76	7.389%	$14.7767	$14.78	$14.80	$14.80
Purchase #7	$90.88	10.282%	$100.2243	$100.22	$100.20	$100.20
7 purchase totals =	$860.32		$954.2896	$954.28	$954.25	$954.30