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	$18.58	10.248%	$20.4841	$20.48	$20.50	$20.50
Purchase #2	$73.94	5.861%	$78.2736	$78.27	$78.25	$78.30
Purchase #3	$167.88	13.291%	$190.1929	$190.19	$190.20	$190.20
Purchase #4	$99.25	13.246%	$112.3967	$112.40	$112.40	$112.40
Purchase #5	$200.66	7.461%	$215.6312	$215.63	$215.65	$215.60
Purchase #6	$131.65	8.207%	$142.4545	$142.45	$142.45	$142.50
Purchase #7	$85.51	5.850%	$90.5123	$90.51	$90.50	$90.50
7 purchase totals =	$777.47		$849.9453	$849.93	$849.95	$850.00