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	$24.38	10.291%	$26.8889	$26.89	$26.90	$26.90
Purchase #2	$83.59	8.397%	$90.6091	$90.61	$90.60	$90.60
Purchase #3	$87.45	10.762%	$96.8614	$96.86	$96.85	$96.90
Purchase #4	$78.29	5.581%	$82.6594	$82.66	$82.65	$82.70
Purchase #5	$213.87	6.434%	$227.6304	$227.63	$227.65	$227.60
Purchase #6	$142.48	4.202%	$148.467	$148.47	$148.45	$148.50
Purchase #7	$145.76	10.634%	$161.2601	$161.26	$161.25	$161.30
7 purchase totals =	$775.82		$834.3763	$834.38	$834.35	$834.50