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	$246.73	13.824%	$280.838	$280.84	$280.85	$280.80
Purchase #2	$6.52	11.676%	$7.2813	$7.28	$7.30	$7.30
Purchase #3	$202.57	10.311%	$223.457	$223.46	$223.45	$223.50
Purchase #4	$27.48	8.730%	$29.879	$29.88	$29.90	$29.90
Purchase #5	$71.57	5.559%	$75.5486	$75.55	$75.55	$75.50
Purchase #6	$66.78	9.196%	$72.9211	$72.92	$72.90	$72.90
Purchase #7	$158.42	4.849%	$166.1018	$166.10	$166.10	$166.10
7 purchase totals =	$780.07		$856.0268	$856.03	$856.05	$856.00