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	$27.83	5.866%	$29.4625	$29.46	$29.45	$29.50
Purchase #2	$125.66	9.477%	$137.5688	$137.57	$137.55	$137.60
Purchase #3	$228.99	9.209%	$250.0777	$250.08	$250.10	$250.10
Purchase #4	$180.77	10.317%	$199.42	$199.42	$199.40	$199.40
Purchase #5	$135.44	6.420%	$144.1352	$144.14	$144.15	$144.10
Purchase #6	$123.42	7.269%	$132.3914	$132.39	$132.40	$132.40
Purchase #7	$83.52	8.196%	$90.3653	$90.37	$90.35	$90.40
7 purchase totals =	$905.63		$983.4209	$983.43	$983.40	$983.50