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	$54.58	9.647%	$59.8453	$59.85	$59.85	$59.80
Purchase #2	$178.59	12.359%	$200.6619	$200.66	$200.65	$200.70
Purchase #3	$199.40	8.217%	$215.7847	$215.78	$215.80	$215.80
Purchase #4	$159.93	5.308%	$168.4191	$168.42	$168.40	$168.40
Purchase #5	$80.59	7.866%	$86.9292	$86.93	$86.95	$86.90
Purchase #6	$27.59	12.394%	$31.0095	$31.01	$31.00	$31.00
Purchase #7	$204.79	6.363%	$217.8208	$217.82	$217.80	$217.80
7 purchase totals =	$905.47		$980.4705	$980.47	$980.45	$980.40