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	$224.72	13.648%	$255.3898	$255.39	$255.40	$255.40
Purchase #2	$43.27	3.284%	$44.691	$44.69	$44.70	$44.70
Purchase #3	$63.27	4.715%	$66.2532	$66.25	$66.25	$66.30
Purchase #4	$28.77	8.604%	$31.2454	$31.25	$31.25	$31.20
Purchase #5	$11.93	10.545%	$13.188	$13.19	$13.20	$13.20
Purchase #6	$103.72	13.330%	$117.5459	$117.55	$117.55	$117.50
Purchase #7	$20.57	7.619%	$22.1372	$22.14	$22.15	$22.10
7 purchase totals =	$496.25		$550.4505	$550.46	$550.50	$550.40