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	$26.78	11.461%	$29.8493	$29.85	$29.85	$29.80
Purchase #2	$43.86	3.111%	$45.2245	$45.22	$45.20	$45.20
Purchase #3	$221.80	9.354%	$242.5472	$242.55	$242.55	$242.50
Purchase #4	$249.75	6.606%	$266.2485	$266.25	$266.25	$266.20
Purchase #5	$192.90	10.105%	$212.3925	$212.39	$212.40	$212.40
Purchase #6	$65.85	8.378%	$71.3669	$71.37	$71.35	$71.40
Purchase #7	$120.99	8.597%	$131.3915	$131.39	$131.40	$131.40
7 purchase totals =	$921.93		$999.0204	$999.02	$999.00	$998.90