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	$37.83	11.265%	$42.0915	$42.09	$42.10	$42.10
Purchase #2	$82.34	9.756%	$90.3731	$90.37	$90.35	$90.40
Purchase #3	$23.85	12.584%	$26.8513	$26.85	$26.85	$26.90
Purchase #4	$117.87	11.661%	$131.6148	$131.61	$131.60	$131.60
Purchase #5	$136.42	11.310%	$151.8491	$151.85	$151.85	$151.80
Purchase #6	$170.61	3.798%	$177.0898	$177.09	$177.10	$177.10
Purchase #7	$242.97	7.186%	$260.4298	$260.43	$260.45	$260.40
7 purchase totals =	$811.89		$880.2994	$880.29	$880.30	$880.30