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	$85.29	9.794%	$93.6433	$93.64	$93.65	$93.60
Purchase #2	$116.83	9.529%	$127.9627	$127.96	$127.95	$128.00
Purchase #3	$190.78	12.444%	$214.5207	$214.52	$214.50	$214.50
Purchase #4	$140.80	3.349%	$145.5154	$145.52	$145.50	$145.50
Purchase #5	$81.95	7.147%	$87.807	$87.81	$87.80	$87.80
Purchase #6	$56.66	10.476%	$62.5957	$62.60	$62.60	$62.60
Purchase #7	$117.40	12.301%	$131.8414	$131.84	$131.85	$131.80
7 purchase totals =	$789.71		$863.8862	$863.89	$863.85	$863.80