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	$240.67	6.725%	$256.8551	$256.86	$256.85	$256.90
Purchase #2	$39.71	4.118%	$41.3453	$41.35	$41.35	$41.30
Purchase #3	$79.26	5.553%	$83.6613	$83.66	$83.65	$83.70
Purchase #4	$16.38	9.240%	$17.8935	$17.89	$17.90	$17.90
Purchase #5	$166.26	11.763%	$185.8172	$185.82	$185.80	$185.80
Purchase #6	$99.90	5.587%	$105.4814	$105.48	$105.50	$105.50
Purchase #7	$185.54	3.387%	$191.8242	$191.82	$191.80	$191.80
7 purchase totals =	$827.72		$882.8780	$882.88	$882.85	$882.90