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	$226.34	4.517%	$236.5638	$236.56	$236.55	$236.60
Purchase #2	$161.71	11.757%	$180.7222	$180.72	$180.70	$180.70
Purchase #3	$25.52	10.174%	$28.1164	$28.12	$28.10	$28.10
Purchase #4	$199.75	13.696%	$227.1078	$227.11	$227.10	$227.10
Purchase #5	$18.78	10.846%	$20.8169	$20.82	$20.80	$20.80
Purchase #6	$87.53	3.581%	$90.6644	$90.66	$90.65	$90.70
Purchase #7	$94.45	9.556%	$103.4756	$103.48	$103.50	$103.50
7 purchase totals =	$814.08		$887.4671	$887.47	$887.40	$887.50