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	$242.50	9.509%	$265.5593	$265.56	$265.55	$265.60
Purchase #2	$187.60	3.725%	$194.5881	$194.59	$194.60	$194.60
Purchase #3	$133.81	13.342%	$151.6629	$151.66	$151.65	$151.70
Purchase #4	$48.44	10.327%	$53.4424	$53.44	$53.45	$53.40
Purchase #5	$35.65	4.275%	$37.174	$37.17	$37.15	$37.20
Purchase #6	$205.60	10.380%	$226.9413	$226.94	$226.95	$226.90
Purchase #7	$149.83	13.656%	$170.2908	$170.29	$170.30	$170.30
7 purchase totals =	$1,003.43		$1,099.6588	$1,099.65	$1,099.65	$1,099.70