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	$15.91	7.337%	$17.0773	$17.08	$17.10	$17.10
Purchase #2	$20.60	6.684%	$21.9769	$21.98	$22.00	$22.00
Purchase #3	$163.39	5.628%	$172.5856	$172.59	$172.60	$172.60
Purchase #4	$114.84	11.105%	$127.593	$127.59	$127.60	$127.60
Purchase #5	$131.54	3.487%	$136.1268	$136.13	$136.15	$136.10
Purchase #6	$33.50	11.106%	$37.2205	$37.22	$37.20	$37.20
Purchase #7	$146.93	5.557%	$155.0949	$155.09	$155.10	$155.10
7 purchase totals =	$626.71		$667.6750	$667.68	$667.75	$667.70