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	$32.89	6.643%	$35.0749	$35.07	$35.05	$35.10
Purchase #2	$161.52	3.296%	$166.8437	$166.84	$166.85	$166.80
Purchase #3	$126.33	8.806%	$137.4546	$137.45	$137.45	$137.50
Purchase #4	$185.95	5.336%	$195.8723	$195.87	$195.85	$195.90
Purchase #5	$126.33	3.269%	$130.4597	$130.46	$130.45	$130.50
Purchase #6	$163.58	5.314%	$172.2726	$172.27	$172.25	$172.30
Purchase #7	$132.83	4.712%	$139.0889	$139.09	$139.10	$139.10
7 purchase totals =	$929.43		$977.0667	$977.05	$977.00	$977.20