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	$84.98	6.376%	$90.3983	$90.40	$90.40	$90.40
Purchase #2	$192.62	13.103%	$217.859	$217.86	$217.85	$217.90
Purchase #3	$220.42	8.692%	$239.5789	$239.58	$239.60	$239.60
Purchase #4	$48.57	6.119%	$51.542	$51.54	$51.55	$51.50
Purchase #5	$54.33	9.429%	$59.4528	$59.45	$59.45	$59.50
Purchase #6	$78.80	9.714%	$86.4546	$86.45	$86.45	$86.50
Purchase #7	$97.90	3.784%	$101.6045	$101.60	$101.60	$101.60
7 purchase totals =	$777.62		$846.8901	$846.88	$846.90	$847.00