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	$134.90	5.545%	$142.3802	$142.38	$142.40	$142.40
Purchase #2	$69.38	12.827%	$78.2794	$78.28	$78.30	$78.30
Purchase #3	$41.98	4.289%	$43.7805	$43.78	$43.80	$43.80
Purchase #4	$240.29	13.147%	$271.8809	$271.88	$271.90	$271.90
Purchase #5	$16.34	11.309%	$18.1879	$18.19	$18.20	$18.20
Purchase #6	$43.81	10.635%	$48.4692	$48.47	$48.45	$48.50
Purchase #7	$180.49	11.874%	$201.9214	$201.92	$201.90	$201.90
7 purchase totals =	$727.19		$804.8995	$804.90	$804.95	$805.00