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	$131.72	9.763%	$144.5798	$144.58	$144.60	$144.60
Purchase #2	$92.83	13.118%	$105.0074	$105.01	$105.00	$105.00
Purchase #3	$84.92	10.435%	$93.7814	$93.78	$93.80	$93.80
Purchase #4	$6.38	13.605%	$7.248	$7.25	$7.25	$7.20
Purchase #5	$171.92	9.105%	$187.5733	$187.57	$187.55	$187.60
Purchase #6	$136.92	3.757%	$142.0641	$142.06	$142.05	$142.10
Purchase #7	$234.25	6.354%	$249.1342	$249.13	$249.15	$249.10
7 purchase totals =	$858.94		$929.3882	$929.38	$929.40	$929.40