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	$10.47	9.281%	$11.4417	$11.44	$11.45	$11.40
Purchase #2	$36.99	10.660%	$40.9331	$40.93	$40.95	$40.90
Purchase #3	$233.51	13.231%	$264.4057	$264.41	$264.40	$264.40
Purchase #4	$51.59	6.367%	$54.8747	$54.87	$54.85	$54.90
Purchase #5	$159.59	5.784%	$168.8207	$168.82	$168.80	$168.80
Purchase #6	$64.38	12.357%	$72.3354	$72.34	$72.35	$72.30
Purchase #7	$231.70	11.342%	$257.9794	$257.98	$258.00	$258.00
7 purchase totals =	$788.23		$870.7907	$870.79	$870.80	$870.70