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	$90.34	11.653%	$100.8673	$100.87	$100.85	$100.90
Purchase #2	$231.57	12.817%	$261.2503	$261.25	$261.25	$261.30
Purchase #3	$73.76	10.653%	$81.6177	$81.62	$81.60	$81.60
Purchase #4	$139.74	9.397%	$152.8714	$152.87	$152.85	$152.90
Purchase #5	$152.83	7.646%	$164.5154	$164.52	$164.50	$164.50
Purchase #6	$133.82	4.491%	$139.8299	$139.83	$139.85	$139.80
Purchase #7	$194.87	11.804%	$217.8725	$217.87	$217.85	$217.90
7 purchase totals =	$1,016.93		$1,118.8245	$1,118.83	$1,118.75	$1,118.90