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	$248.96	6.493%	$265.125	$265.13	$265.15	$265.10
Purchase #2	$167.48	9.536%	$183.4509	$183.45	$183.45	$183.50
Purchase #3	$10.36	13.536%	$11.7623	$11.76	$11.75	$11.80
Purchase #4	$156.40	9.641%	$171.4785	$171.48	$171.50	$171.50
Purchase #5	$144.98	13.721%	$164.8727	$164.87	$164.85	$164.90
Purchase #6	$80.82	7.531%	$86.9066	$86.91	$86.90	$86.90
Purchase #7	$13.31	12.796%	$15.0131	$15.01	$15.00	$15.00
7 purchase totals =	$822.31		$898.6091	$898.61	$898.60	$898.70