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	$131.75	8.862%	$143.4257	$143.43	$143.45	$143.40
Purchase #2	$58.93	12.595%	$66.3522	$66.35	$66.35	$66.40
Purchase #3	$177.66	10.350%	$196.0478	$196.05	$196.05	$196.00
Purchase #4	$129.53	8.498%	$140.5375	$140.54	$140.55	$140.50
Purchase #5	$134.56	13.732%	$153.0378	$153.04	$153.05	$153.00
Purchase #6	$45.38	13.159%	$51.3516	$51.35	$51.35	$51.40
Purchase #7	$170.90	5.630%	$180.5217	$180.52	$180.50	$180.50
7 purchase totals =	$848.71		$931.2743	$931.28	$931.30	$931.20