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	$30.71	3.493%	$31.7827	$31.78	$31.80	$31.80
Purchase #2	$51.46	8.841%	$56.0096	$56.01	$56.00	$56.00
Purchase #3	$163.89	13.758%	$186.438	$186.44	$186.45	$186.40
Purchase #4	$116.31	4.424%	$121.4556	$121.46	$121.45	$121.50
Purchase #5	$139.72	8.741%	$151.9329	$151.93	$151.95	$151.90
Purchase #6	$122.86	13.443%	$139.3761	$139.38	$139.40	$139.40
Purchase #7	$213.36	13.230%	$241.5875	$241.59	$241.60	$241.60
7 purchase totals =	$838.31		$928.5824	$928.59	$928.65	$928.60