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	$105.81	3.405%	$109.4128	$109.41	$109.40	$109.40
Purchase #2	$112.94	13.692%	$128.4037	$128.40	$128.40	$128.40
Purchase #3	$39.66	10.659%	$43.8874	$43.89	$43.90	$43.90
Purchase #4	$128.52	6.172%	$136.4523	$136.45	$136.45	$136.50
Purchase #5	$49.69	6.665%	$53.0018	$53.00	$53.00	$53.00
Purchase #6	$101.42	13.276%	$114.8845	$114.88	$114.90	$114.90
Purchase #7	$51.44	11.763%	$57.4909	$57.49	$57.50	$57.50
7 purchase totals =	$589.48		$643.5334	$643.52	$643.55	$643.60