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	$80.45	7.509%	$86.491	$86.49	$86.50	$86.50
Purchase #2	$151.89	13.870%	$172.9571	$172.96	$172.95	$173.00
Purchase #3	$190.78	8.316%	$206.6453	$206.65	$206.65	$206.60
Purchase #4	$159.92	3.846%	$166.0705	$166.07	$166.05	$166.10
Purchase #5	$192.37	12.592%	$216.5932	$216.59	$216.60	$216.60
Purchase #6	$208.27	3.611%	$215.7906	$215.79	$215.80	$215.80
Purchase #7	$20.33	4.410%	$21.2266	$21.23	$21.25	$21.20
7 purchase totals =	$1,004.01		$1,085.7743	$1,085.78	$1,085.80	$1,085.80