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	$85.30	9.812%	$93.6696	$93.67	$93.65	$93.70
Purchase #2	$204.37	13.312%	$231.5757	$231.58	$231.60	$231.60
Purchase #3	$127.81	5.522%	$134.8677	$134.87	$134.85	$134.90
Purchase #4	$113.81	12.663%	$128.2218	$128.22	$128.20	$128.20
Purchase #5	$139.29	4.486%	$145.5385	$145.54	$145.55	$145.50
Purchase #6	$103.45	8.238%	$111.9722	$111.97	$111.95	$112.00
Purchase #7	$120.82	9.684%	$132.5202	$132.52	$132.50	$132.50
7 purchase totals =	$894.85		$978.3657	$978.37	$978.30	$978.40