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	$248.43	11.657%	$277.3895	$277.39	$277.40	$277.40
Purchase #2	$205.53	6.129%	$218.1269	$218.13	$218.15	$218.10
Purchase #3	$100.45	10.750%	$111.2484	$111.25	$111.25	$111.20
Purchase #4	$131.97	13.493%	$149.7767	$149.78	$149.80	$149.80
Purchase #5	$178.42	12.354%	$200.462	$200.46	$200.45	$200.50
Purchase #6	$38.38	13.125%	$43.4174	$43.42	$43.40	$43.40
Purchase #7	$78.96	4.471%	$82.4903	$82.49	$82.50	$82.50
7 purchase totals =	$982.14		$1,082.9112	$1,082.92	$1,082.95	$1,082.90