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	$105.92	6.611%	$112.9224	$112.92	$112.90	$112.90
Purchase #2	$165.83	7.215%	$177.7946	$177.79	$177.80	$177.80
Purchase #3	$230.46	12.176%	$258.5208	$258.52	$258.50	$258.50
Purchase #4	$40.98	3.589%	$42.4508	$42.45	$42.45	$42.50
Purchase #5	$77.32	12.288%	$86.8211	$86.82	$86.80	$86.80
Purchase #6	$101.54	9.491%	$111.1772	$111.18	$111.20	$111.20
Purchase #7	$48.41	13.797%	$55.0891	$55.09	$55.10	$55.10
7 purchase totals =	$770.46		$844.7760	$844.77	$844.75	$844.80