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	$19.71	8.712%	$21.4271	$21.43	$21.45	$21.40
Purchase #2	$217.68	3.560%	$225.4294	$225.43	$225.45	$225.40
Purchase #3	$77.32	7.630%	$83.2195	$83.22	$83.20	$83.20
Purchase #4	$127.43	12.451%	$143.2963	$143.30	$143.30	$143.30
Purchase #5	$106.88	4.186%	$111.354	$111.35	$111.35	$111.40
Purchase #6	$113.56	9.105%	$123.8996	$123.90	$123.90	$123.90
Purchase #7	$79.51	4.300%	$82.9289	$82.93	$82.95	$82.90
7 purchase totals =	$742.09		$791.5548	$791.56	$791.60	$791.50