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	$109.88	5.856%	$116.3146	$116.31	$116.30	$116.30
Purchase #2	$118.54	10.677%	$131.1965	$131.20	$131.20	$131.20
Purchase #3	$100.72	12.334%	$113.1428	$113.14	$113.15	$113.10
Purchase #4	$57.80	8.716%	$62.8378	$62.84	$62.85	$62.80
Purchase #5	$75.89	3.299%	$78.3936	$78.39	$78.40	$78.40
Purchase #6	$105.83	8.788%	$115.1303	$115.13	$115.15	$115.10
Purchase #7	$121.75	8.743%	$132.3946	$132.39	$132.40	$132.40
7 purchase totals =	$690.41		$749.4102	$749.40	$749.45	$749.30