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	$236.97	12.501%	$266.5936	$266.59	$266.60	$266.60
Purchase #2	$159.48	12.787%	$179.8727	$179.87	$179.85	$179.90
Purchase #3	$103.58	13.737%	$117.8088	$117.81	$117.80	$117.80
Purchase #4	$51.68	3.743%	$53.6144	$53.61	$53.60	$53.60
Purchase #5	$133.83	3.516%	$138.5355	$138.54	$138.55	$138.50
Purchase #6	$245.97	9.471%	$269.2658	$269.27	$269.25	$269.30
Purchase #7	$79.86	13.436%	$90.59	$90.59	$90.60	$90.60
7 purchase totals =	$1,011.37		$1,116.2808	$1,116.28	$1,116.25	$1,116.30