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	$231.52	12.109%	$259.5548	$259.55	$259.55	$259.60
Purchase #2	$235.39	11.390%	$262.2009	$262.20	$262.20	$262.20
Purchase #3	$41.55	3.837%	$43.1443	$43.14	$43.15	$43.10
Purchase #4	$62.65	6.193%	$66.5299	$66.53	$66.55	$66.50
Purchase #5	$97.59	12.380%	$109.6716	$109.67	$109.65	$109.70
Purchase #6	$125.97	11.139%	$140.0018	$140.00	$140.00	$140.00
Purchase #7	$100.34	8.408%	$108.7766	$108.78	$108.80	$108.80
7 purchase totals =	$895.01		$989.8799	$989.87	$989.90	$989.90