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	$52.79	12.694%	$59.4912	$59.49	$59.50	$59.50
Purchase #2	$14.69	5.208%	$15.4551	$15.46	$15.45	$15.50
Purchase #3	$82.37	11.523%	$91.8615	$91.86	$91.85	$91.90
Purchase #4	$48.39	5.491%	$51.0471	$51.05	$51.05	$51.00
Purchase #5	$193.74	8.331%	$209.8805	$209.88	$209.90	$209.90
Purchase #6	$112.32	4.324%	$117.1767	$117.18	$117.20	$117.20
Purchase #7	$128.66	8.497%	$139.5922	$139.59	$139.60	$139.60
7 purchase totals =	$632.96		$684.5043	$684.51	$684.55	$684.60