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	$57.77	10.221%	$63.6747	$63.67	$63.65	$63.70
Purchase #2	$17.56	13.676%	$19.9615	$19.96	$19.95	$20.00
Purchase #3	$177.82	4.672%	$186.1278	$186.13	$186.15	$186.10
Purchase #4	$75.54	11.700%	$84.3782	$84.38	$84.40	$84.40
Purchase #5	$55.85	10.263%	$61.5819	$61.58	$61.60	$61.60
Purchase #6	$33.95	11.613%	$37.8926	$37.89	$37.90	$37.90
Purchase #7	$200.52	13.139%	$226.8663	$226.87	$226.85	$226.90
7 purchase totals =	$619.01		$680.4830	$680.48	$680.50	$680.60