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	$66.80	8.137%	$72.2355	$72.24	$72.25	$72.20
Purchase #2	$199.42	11.300%	$221.9545	$221.95	$221.95	$222.00
Purchase #3	$32.29	10.255%	$35.6013	$35.60	$35.60	$35.60
Purchase #4	$142.66	3.212%	$147.2422	$147.24	$147.25	$147.20
Purchase #5	$137.65	13.257%	$155.8983	$155.90	$155.90	$155.90
Purchase #6	$127.26	12.863%	$143.6295	$143.63	$143.65	$143.60
Purchase #7	$39.78	7.776%	$42.8733	$42.87	$42.85	$42.90
7 purchase totals =	$745.86		$819.4346	$819.43	$819.45	$819.40