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	$117.97	8.856%	$128.4174	$128.42	$128.40	$128.40
Purchase #2	$49.70	12.439%	$55.8822	$55.88	$55.90	$55.90
Purchase #3	$38.77	12.418%	$43.5845	$43.58	$43.60	$43.60
Purchase #4	$17.53	4.171%	$18.2612	$18.26	$18.25	$18.30
Purchase #5	$124.45	7.578%	$133.8808	$133.88	$133.90	$133.90
Purchase #6	$123.45	6.621%	$131.6236	$131.62	$131.60	$131.60
Purchase #7	$142.45	8.204%	$154.1366	$154.14	$154.15	$154.10
7 purchase totals =	$614.32		$665.7863	$665.78	$665.80	$665.80