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	$34.75	8.193%	$37.5971	$37.60	$37.60	$37.60
Purchase #2	$89.35	11.605%	$99.7191	$99.72	$99.70	$99.70
Purchase #3	$49.97	12.247%	$56.0898	$56.09	$56.10	$56.10
Purchase #4	$57.30	10.841%	$63.5119	$63.51	$63.50	$63.50
Purchase #5	$46.93	9.556%	$51.4146	$51.41	$51.40	$51.40
Purchase #6	$101.72	12.353%	$114.2855	$114.29	$114.30	$114.30
Purchase #7	$87.35	12.752%	$98.4889	$98.49	$98.50	$98.50
7 purchase totals =	$467.37		$521.1069	$521.11	$521.10	$521.10