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	$226.28	13.555%	$256.9523	$256.95	$256.95	$257.00
Purchase #2	$38.93	6.795%	$41.5753	$41.58	$41.60	$41.60
Purchase #3	$102.78	8.680%	$111.7013	$111.70	$111.70	$111.70
Purchase #4	$79.57	4.206%	$82.9167	$82.92	$82.90	$82.90
Purchase #5	$137.61	6.281%	$146.2533	$146.25	$146.25	$146.30
Purchase #6	$199.61	12.378%	$224.3177	$224.32	$224.30	$224.30
Purchase #7	$69.89	4.177%	$72.8093	$72.81	$72.80	$72.80
7 purchase totals =	$854.67		$936.5259	$936.53	$936.50	$936.60