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	$9.64	6.510%	$10.2676	$10.27	$10.25	$10.30
Purchase #2	$120.83	7.305%	$129.6566	$129.66	$129.65	$129.70
Purchase #3	$163.88	13.862%	$186.597	$186.60	$186.60	$186.60
Purchase #4	$161.49	13.598%	$183.4494	$183.45	$183.45	$183.40
Purchase #5	$174.78	12.316%	$196.3059	$196.31	$196.30	$196.30
Purchase #6	$63.78	13.230%	$72.2181	$72.22	$72.20	$72.20
Purchase #7	$9.68	11.691%	$10.8117	$10.81	$10.80	$10.80
7 purchase totals =	$704.08		$789.3063	$789.32	$789.25	$789.30