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	$60.94	8.281%	$65.9864	$65.99	$66.00	$66.00
Purchase #2	$250.60	8.766%	$272.5676	$272.57	$272.55	$272.60
Purchase #3	$85.78	11.761%	$95.8686	$95.87	$95.85	$95.90
Purchase #4	$85.81	5.697%	$90.6986	$90.70	$90.70	$90.70
Purchase #5	$5.98	4.573%	$6.2535	$6.25	$6.25	$6.30
Purchase #6	$139.44	12.360%	$156.6748	$156.67	$156.65	$156.70
Purchase #7	$50.89	7.166%	$54.5368	$54.54	$54.55	$54.50
7 purchase totals =	$679.44		$742.5863	$742.59	$742.55	$742.70