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	$62.68	10.316%	$69.1461	$69.15	$69.15	$69.10
Purchase #2	$93.88	10.278%	$103.529	$103.53	$103.55	$103.50
Purchase #3	$133.86	7.184%	$143.4765	$143.48	$143.50	$143.50
Purchase #4	$175.27	13.704%	$199.289	$199.29	$199.30	$199.30
Purchase #5	$14.79	4.526%	$15.4594	$15.46	$15.45	$15.50
Purchase #6	$234.99	8.704%	$255.4435	$255.44	$255.45	$255.40
Purchase #7	$39.82	13.646%	$45.2538	$45.25	$45.25	$45.30
7 purchase totals =	$755.29		$831.5973	$831.60	$831.65	$831.60