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	$142.89	5.153%	$150.2531	$150.25	$150.25	$150.30
Purchase #2	$119.65	10.407%	$132.102	$132.10	$132.10	$132.10
Purchase #3	$190.87	13.177%	$216.0209	$216.02	$216.00	$216.00
Purchase #4	$83.96	7.834%	$90.5374	$90.54	$90.55	$90.50
Purchase #5	$32.56	5.606%	$34.3853	$34.39	$34.40	$34.40
Purchase #6	$250.52	11.605%	$279.5928	$279.59	$279.60	$279.60
Purchase #7	$51.80	9.134%	$56.5314	$56.53	$56.55	$56.50
7 purchase totals =	$872.25		$959.4229	$959.42	$959.45	$959.40