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	$161.59	5.157%	$169.9232	$169.92	$169.90	$169.90
Purchase #2	$227.31	8.619%	$246.9018	$246.90	$246.90	$246.90
Purchase #3	$126.33	8.119%	$136.5867	$136.59	$136.60	$136.60
Purchase #4	$8.94	12.416%	$10.05	$10.05	$10.05	$10.10
Purchase #5	$108.41	5.483%	$114.3541	$114.35	$114.35	$114.40
Purchase #6	$196.42	11.337%	$218.6881	$218.69	$218.70	$218.70
Purchase #7	$40.89	7.197%	$43.8329	$43.83	$43.85	$43.80
7 purchase totals =	$869.89		$940.3368	$940.33	$940.35	$940.40