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	$199.80	4.232%	$208.2555	$208.26	$208.25	$208.30
Purchase #2	$83.59	8.658%	$90.8272	$90.83	$90.85	$90.80
Purchase #3	$197.75	12.390%	$222.2512	$222.25	$222.25	$222.30
Purchase #4	$44.91	6.665%	$47.9033	$47.90	$47.90	$47.90
Purchase #5	$17.82	4.849%	$18.6841	$18.68	$18.70	$18.70
Purchase #6	$133.73	7.322%	$143.5217	$143.52	$143.50	$143.50
Purchase #7	$230.41	6.801%	$246.0802	$246.08	$246.10	$246.10
7 purchase totals =	$908.01		$977.5232	$977.52	$977.55	$977.60