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	$137.50	13.691%	$156.3251	$156.33	$156.35	$156.30
Purchase #2	$38.80	6.728%	$41.4105	$41.41	$41.40	$41.40
Purchase #3	$194.83	10.301%	$214.8994	$214.90	$214.90	$214.90
Purchase #4	$22.50	13.395%	$25.5139	$25.51	$25.50	$25.50
Purchase #5	$6.94	10.157%	$7.6449	$7.64	$7.65	$7.60
Purchase #6	$247.32	4.663%	$258.8525	$258.85	$258.85	$258.90
Purchase #7	$233.45	9.376%	$255.3383	$255.34	$255.35	$255.30
7 purchase totals =	$881.34		$959.9846	$959.98	$960.00	$959.90