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	$29.74	12.792%	$33.5443	$33.54	$33.55	$33.50
Purchase #2	$78.43	13.504%	$89.0212	$89.02	$89.00	$89.00
Purchase #3	$46.28	9.815%	$50.8224	$50.82	$50.80	$50.80
Purchase #4	$38.90	8.105%	$42.0528	$42.05	$42.05	$42.10
Purchase #5	$19.78	3.817%	$20.535	$20.54	$20.55	$20.50
Purchase #6	$120.30	5.593%	$127.0284	$127.03	$127.05	$127.00
Purchase #7	$104.47	12.355%	$117.3773	$117.38	$117.40	$117.40
7 purchase totals =	$437.90		$480.3814	$480.38	$480.40	$480.30