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	$126.94	10.329%	$140.0516	$140.05	$140.05	$140.10
Purchase #2	$93.67	4.176%	$97.5817	$97.58	$97.60	$97.60
Purchase #3	$130.44	9.143%	$142.3661	$142.37	$142.35	$142.40
Purchase #4	$30.80	5.861%	$32.6052	$32.61	$32.60	$32.60
Purchase #5	$42.92	5.105%	$45.1111	$45.11	$45.10	$45.10
Purchase #6	$32.51	6.203%	$34.5266	$34.53	$34.55	$34.50
Purchase #7	$30.84	4.604%	$32.2599	$32.26	$32.25	$32.30
7 purchase totals =	$488.12		$524.5022	$524.51	$524.50	$524.60