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	$5.54	8.450%	$6.0081	$6.01	$6.00	$6.00
Purchase #2	$81.73	10.599%	$90.3926	$90.39	$90.40	$90.40
Purchase #3	$60.85	12.172%	$68.2567	$68.26	$68.25	$68.30
Purchase #4	$117.58	4.614%	$123.0051	$123.01	$123.00	$123.00
Purchase #5	$23.83	10.602%	$26.3565	$26.36	$26.35	$26.40
Purchase #6	$144.46	5.412%	$152.2782	$152.28	$152.30	$152.30
Purchase #7	$87.79	8.531%	$95.2794	$95.28	$95.30	$95.30
7 purchase totals =	$521.78		$561.5766	$561.59	$561.60	$561.70