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	$59.99	13.197%	$67.9069	$67.91	$67.90	$67.90
Purchase #2	$248.67	5.548%	$262.4662	$262.47	$262.45	$262.50
Purchase #3	$194.34	12.420%	$218.477	$218.48	$218.50	$218.50
Purchase #4	$41.49	9.422%	$45.3992	$45.40	$45.40	$45.40
Purchase #5	$41.79	12.245%	$46.9072	$46.91	$46.90	$46.90
Purchase #6	$17.28	9.273%	$18.8824	$18.88	$18.90	$18.90
Purchase #7	$87.32	8.211%	$94.4898	$94.49	$94.50	$94.50
7 purchase totals =	$690.88		$754.5287	$754.54	$754.55	$754.60