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	$6.69	13.660%	$7.6039	$7.60	$7.60	$7.60
Purchase #2	$196.49	12.676%	$221.3971	$221.40	$221.40	$221.40
Purchase #3	$130.46	7.152%	$139.7905	$139.79	$139.80	$139.80
Purchase #4	$220.40	6.765%	$235.3101	$235.31	$235.30	$235.30
Purchase #5	$212.69	5.555%	$224.5049	$224.50	$224.50	$224.50
Purchase #6	$140.57	8.526%	$152.555	$152.56	$152.55	$152.60
Purchase #7	$242.98	6.598%	$259.0118	$259.01	$259.00	$259.00
7 purchase totals =	$1,150.28		$1,240.1733	$1,240.17	$1,240.15	$1,240.20