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	$100.60	4.778%	$105.4067	$105.41	$105.40	$105.40
Purchase #2	$14.31	8.462%	$15.5209	$15.52	$15.50	$15.50
Purchase #3	$131.49	6.377%	$139.8751	$139.88	$139.90	$139.90
Purchase #4	$164.89	6.829%	$176.1503	$176.15	$176.15	$176.20
Purchase #5	$37.71	11.576%	$42.0753	$42.08	$42.10	$42.10
Purchase #6	$127.80	10.601%	$141.3481	$141.35	$141.35	$141.30
Purchase #7	$211.84	12.313%	$237.9239	$237.92	$237.90	$237.90
7 purchase totals =	$788.64		$858.3003	$858.31	$858.30	$858.30