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	$214.28	12.666%	$241.4207	$241.42	$241.40	$241.40
Purchase #2	$243.54	6.316%	$258.922	$258.92	$258.90	$258.90
Purchase #3	$132.45	8.338%	$143.4937	$143.49	$143.50	$143.50
Purchase #4	$176.83	9.105%	$192.9304	$192.93	$192.95	$192.90
Purchase #5	$132.71	4.810%	$139.0934	$139.09	$139.10	$139.10
Purchase #6	$39.92	6.834%	$42.6481	$42.65	$42.65	$42.60
Purchase #7	$44.45	7.633%	$47.8429	$47.84	$47.85	$47.80
7 purchase totals =	$984.18		$1,066.3512	$1,066.34	$1,066.35	$1,066.20