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	$228.76	3.326%	$236.3686	$236.37	$236.35	$236.40
Purchase #2	$129.35	13.267%	$146.5109	$146.51	$146.50	$146.50
Purchase #3	$79.86	11.492%	$89.0375	$89.04	$89.05	$89.00
Purchase #4	$86.69	11.697%	$96.8301	$96.83	$96.85	$96.80
Purchase #5	$10.89	10.843%	$12.0708	$12.07	$12.05	$12.10
Purchase #6	$149.55	9.194%	$163.2996	$163.30	$163.30	$163.30
Purchase #7	$72.78	7.859%	$78.4998	$78.50	$78.50	$78.50
7 purchase totals =	$757.88		$822.6173	$822.62	$822.60	$822.60