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	$203.35	11.874%	$227.4958	$227.50	$227.50	$227.50
Purchase #2	$75.38	4.217%	$78.5588	$78.56	$78.55	$78.60
Purchase #3	$71.62	13.704%	$81.4348	$81.43	$81.45	$81.40
Purchase #4	$155.42	10.826%	$172.2458	$172.25	$172.25	$172.20
Purchase #5	$231.39	6.804%	$247.1338	$247.13	$247.15	$247.10
Purchase #6	$91.97	13.716%	$104.5846	$104.58	$104.60	$104.60
Purchase #7	$34.27	13.412%	$38.8663	$38.87	$38.85	$38.90
7 purchase totals =	$863.40		$950.3199	$950.32	$950.35	$950.30