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	$101.84	12.533%	$114.6036	$114.60	$114.60	$114.60
Purchase #2	$74.44	8.665%	$80.8902	$80.89	$80.90	$80.90
Purchase #3	$172.88	11.465%	$192.7007	$192.70	$192.70	$192.70
Purchase #4	$128.58	4.631%	$134.5345	$134.53	$134.55	$134.50
Purchase #5	$40.78	3.163%	$42.0699	$42.07	$42.05	$42.10
Purchase #6	$202.64	12.252%	$227.4675	$227.47	$227.45	$227.50
Purchase #7	$122.90	3.870%	$127.6562	$127.66	$127.65	$127.70
7 purchase totals =	$844.06		$919.9226	$919.92	$919.90	$920.00