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	$34.82	13.172%	$39.4065	$39.41	$39.40	$39.40
Purchase #2	$157.58	10.153%	$173.5791	$173.58	$173.60	$173.60
Purchase #3	$10.43	13.319%	$11.8192	$11.82	$11.80	$11.80
Purchase #4	$138.72	4.361%	$144.7696	$144.77	$144.75	$144.80
Purchase #5	$173.93	5.135%	$182.8613	$182.86	$182.85	$182.90
Purchase #6	$42.93	6.287%	$45.629	$45.63	$45.65	$45.60
Purchase #7	$205.44	13.842%	$233.877	$233.88	$233.90	$233.90
7 purchase totals =	$763.85		$831.9417	$831.95	$831.95	$832.00