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	$136.97	6.224%	$145.495	$145.50	$145.50	$145.50
Purchase #2	$161.59	11.701%	$180.4976	$180.50	$180.50	$180.50
Purchase #3	$131.80	11.153%	$146.4997	$146.50	$146.50	$146.50
Purchase #4	$132.93	8.249%	$143.8954	$143.90	$143.90	$143.90
Purchase #5	$52.77	12.739%	$59.4924	$59.49	$59.50	$59.50
Purchase #6	$22.93	13.159%	$25.9474	$25.95	$25.95	$25.90
Purchase #7	$238.61	9.105%	$260.3354	$260.34	$260.35	$260.30
7 purchase totals =	$877.60		$962.1629	$962.18	$962.20	$962.10