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	$112.66	13.105%	$127.4241	$127.42	$127.40	$127.40
Purchase #2	$105.37	7.213%	$112.9703	$112.97	$112.95	$113.00
Purchase #3	$29.27	4.634%	$30.6264	$30.63	$30.65	$30.60
Purchase #4	$219.52	4.126%	$228.5774	$228.58	$228.60	$228.60
Purchase #5	$133.77	7.523%	$143.8335	$143.83	$143.85	$143.80
Purchase #6	$35.32	6.401%	$37.5808	$37.58	$37.60	$37.60
Purchase #7	$140.90	8.483%	$152.8525	$152.85	$152.85	$152.90
7 purchase totals =	$776.81		$833.8650	$833.86	$833.90	$833.90