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	$6.36	8.291%	$6.8873	$6.89	$6.90	$6.90
Purchase #2	$31.95	4.581%	$33.4136	$33.41	$33.40	$33.40
Purchase #3	$152.78	9.195%	$166.8281	$166.83	$166.85	$166.80
Purchase #4	$129.63	10.348%	$143.0441	$143.04	$143.05	$143.00
Purchase #5	$25.50	6.128%	$27.0626	$27.06	$27.05	$27.10
Purchase #6	$153.35	8.637%	$166.5948	$166.59	$166.60	$166.60
Purchase #7	$66.53	8.812%	$72.3926	$72.39	$72.40	$72.40
7 purchase totals =	$566.10		$616.2231	$616.21	$616.25	$616.20