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	$82.83	3.214%	$85.4922	$85.49	$85.50	$85.50
Purchase #2	$131.42	5.455%	$138.589	$138.59	$138.60	$138.60
Purchase #3	$183.27	13.699%	$208.3762	$208.38	$208.40	$208.40
Purchase #4	$208.83	8.542%	$226.6683	$226.67	$226.65	$226.70
Purchase #5	$30.44	11.244%	$33.8627	$33.86	$33.85	$33.90
Purchase #6	$233.98	9.153%	$255.3962	$255.40	$255.40	$255.40
Purchase #7	$85.28	6.806%	$91.0842	$91.08	$91.10	$91.10
7 purchase totals =	$956.05		$1,039.4688	$1,039.47	$1,039.50	$1,039.60