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	$11.97	10.732%	$13.2546	$13.25	$13.25	$13.30
Purchase #2	$85.57	5.698%	$90.4458	$90.45	$90.45	$90.40
Purchase #3	$27.66	10.453%	$30.5513	$30.55	$30.55	$30.60
Purchase #4	$59.83	10.161%	$65.9093	$65.91	$65.90	$65.90
Purchase #5	$169.63	6.462%	$180.5915	$180.59	$180.60	$180.60
Purchase #6	$59.77	3.366%	$61.7819	$61.78	$61.80	$61.80
Purchase #7	$208.75	8.521%	$226.5376	$226.54	$226.55	$226.50
7 purchase totals =	$623.18		$669.0720	$669.07	$669.10	$669.10