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	$126.95	11.714%	$141.8209	$141.82	$141.80	$141.80
Purchase #2	$97.88	4.302%	$102.0908	$102.09	$102.10	$102.10
Purchase #3	$138.86	11.567%	$154.9219	$154.92	$154.90	$154.90
Purchase #4	$90.67	9.815%	$99.5693	$99.57	$99.55	$99.60
Purchase #5	$60.31	4.591%	$63.0788	$63.08	$63.10	$63.10
Purchase #6	$20.37	3.724%	$21.1286	$21.13	$21.15	$21.10
Purchase #7	$71.46	11.784%	$79.8808	$79.88	$79.90	$79.90
7 purchase totals =	$606.50		$662.4911	$662.49	$662.50	$662.50