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	$82.70	8.593%	$89.8064	$89.81	$89.80	$89.80
Purchase #2	$154.49	11.630%	$172.4572	$172.46	$172.45	$172.50
Purchase #3	$153.66	12.691%	$173.161	$173.16	$173.15	$173.20
Purchase #4	$160.60	13.787%	$182.7419	$182.74	$182.75	$182.70
Purchase #5	$37.65	8.552%	$40.8698	$40.87	$40.85	$40.90
Purchase #6	$239.92	13.669%	$272.7147	$272.71	$272.70	$272.70
Purchase #7	$38.70	11.708%	$43.231	$43.23	$43.25	$43.20
7 purchase totals =	$867.72		$974.9820	$974.98	$974.95	$975.00