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	$47.78	5.179%	$50.2545	$50.25	$50.25	$50.30
Purchase #2	$133.55	5.149%	$140.4265	$140.43	$140.45	$140.40
Purchase #3	$120.47	10.404%	$133.0037	$133.00	$133.00	$133.00
Purchase #4	$83.32	8.690%	$90.5605	$90.56	$90.55	$90.60
Purchase #5	$137.49	12.800%	$155.0887	$155.09	$155.10	$155.10
Purchase #6	$122.53	13.794%	$139.4318	$139.43	$139.45	$139.40
Purchase #7	$97.68	5.716%	$103.2634	$103.26	$103.25	$103.30
7 purchase totals =	$742.82		$812.0291	$812.02	$812.05	$812.10