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	$238.53	7.313%	$255.9737	$255.97	$255.95	$256.00
Purchase #2	$117.25	12.545%	$131.959	$131.96	$131.95	$132.00
Purchase #3	$220.52	9.304%	$241.0372	$241.04	$241.05	$241.00
Purchase #4	$98.55	3.367%	$101.8682	$101.87	$101.85	$101.90
Purchase #5	$40.42	8.171%	$43.7227	$43.72	$43.70	$43.70
Purchase #6	$41.45	3.225%	$42.7868	$42.79	$42.80	$42.80
Purchase #7	$45.58	7.735%	$49.1056	$49.11	$49.10	$49.10
7 purchase totals =	$802.30		$866.4532	$866.46	$866.40	$866.50