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	$129.65	11.667%	$144.7763	$144.78	$144.80	$144.80
Purchase #2	$81.42	8.661%	$88.4718	$88.47	$88.45	$88.50
Purchase #3	$79.63	12.241%	$89.3775	$89.38	$89.40	$89.40
Purchase #4	$143.26	10.650%	$158.5172	$158.52	$158.50	$158.50
Purchase #5	$34.93	12.874%	$39.4269	$39.43	$39.45	$39.40
Purchase #6	$61.87	7.866%	$66.7367	$66.74	$66.75	$66.70
Purchase #7	$24.51	6.158%	$26.0193	$26.02	$26.00	$26.00
7 purchase totals =	$555.27		$613.3257	$613.34	$613.35	$613.30