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	$160.34	4.421%	$167.4286	$167.43	$167.45	$167.40
Purchase #2	$216.63	11.665%	$241.8999	$241.90	$241.90	$241.90
Purchase #3	$117.78	11.633%	$131.4813	$131.48	$131.50	$131.50
Purchase #4	$25.70	8.411%	$27.8616	$27.86	$27.85	$27.90
Purchase #5	$179.87	11.678%	$200.8752	$200.88	$200.90	$200.90
Purchase #6	$15.76	11.138%	$17.5153	$17.52	$17.50	$17.50
Purchase #7	$47.95	8.233%	$51.8977	$51.90	$51.90	$51.90
7 purchase totals =	$764.03		$838.9596	$838.97	$839.00	$839.00