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	$132.97	9.387%	$145.4519	$145.45	$145.45	$145.50
Purchase #2	$102.83	11.709%	$114.8704	$114.87	$114.85	$114.90
Purchase #3	$166.35	13.419%	$188.6725	$188.67	$188.65	$188.70
Purchase #4	$69.75	9.565%	$76.4216	$76.42	$76.40	$76.40
Purchase #5	$37.91	10.594%	$41.9262	$41.93	$41.95	$41.90
Purchase #6	$246.43	3.649%	$255.4222	$255.42	$255.40	$255.40
Purchase #7	$111.39	4.856%	$116.7991	$116.80	$116.80	$116.80
7 purchase totals =	$867.63		$939.5639	$939.56	$939.50	$939.60