Taxes are not defined in the US Constitution nor as a general term by any federal statute, but a tax is considered to be a government assessment on property and transactions (e.g. import, sale, transfer of property), assessed to defray the cost of running a government. Governments also charge fees for specific services. Stemming from Proposition 218, California's constitution requires voter approval to increase taxes, but not fees. Article XIII-C defines "tax" as "any levy, charge, or exaction of any kind imposed by a local government except"...
(1) A charge imposed for a specific benefit conferred or privilege
granted directly to the payor that is not provided to those not
charged, and which does not exceed the reasonable costs to the local
government of conferring the benefit or granting the privilege.
(2) A charge imposed for a specific government service or product
provided directly to the payor that is not provided to those not
charged, and which does not exceed the reasonable costs to the local
government of providing the service or product.
(3) A charge imposed for the reasonable regulatory costs to a local
government for issuing licenses and permits, performing
investigations, inspections, and audits, enforcing agricultural
marketing orders, and the administrative enforcement and adjudication
thereof.
(4) A charge imposed for entrance to or use of local government
property, or the purchase, rental, or lease of local government
property.
(5) A fine, penalty, or other monetary charge imposed by the judicial
branch of government or a local government, as a result of a violation
of law.
(6) A charge imposed as a condition of property development.
(7) Assessments and property-related fees imposed in accordance with
the provisions of Article XIII D.
Providing a driver's license or state ID card would not be a "tax" under California's constitution.
TABOR Foundation v. Colorado Bridge Enterprise has some potential relevance for legally defining "tax". The court recites the distinction thusly:
The purpose of a tax is to “provide revenues in order to defray the
general expenses of government as distinguished from the expense of a
specific function or service.” Bloom v. City of Fort Collins, 784
P.2d 304, 307 (Colo.1989). “Unlike a tax, a special fee is not
designed to raise revenues to defray the general expenses of
government, but rather is a charge imposed upon persons or property
for the purpose of defraying the cost of a particular governmental
service.” Barber v. Ritter, 196 P.3d 238, 248 (Colo.2008) (quoting
Bloom, 784 P.2d at 308). Therefore, a fee may be subject to
invalidation as a tax when the principal purpose of the fee is to
raise revenues for general governmental purposes rather than to defray
the expenses of the particular service for which the fee is imposed.
Bloom, 784 P.2d at 308.
“To determine whether a government mandated financial imposition is a
‘fee’ or a ‘tax,’ the dispositive criteria is the primary or dominant
purpose of such imposition at the time the enactment calling for its
collection is passed.” Barber, 196 P.3d at 248
So again, charging for a driver's license or a state ID card would not constitute a "tax" under these interpretations of "tax".
It is hard to know what SCOTUS would rule if the matter came to them. Recall that in National Federation of Independent Business v. Sebelius, it was held that the "teeth" of the individual mandate was held to be a penalty and not a tax, with respect to the Anti-Injunction Act (therefore, the court can hear the case). But then it is a tax (thus authorized under the Tax and Spend Clause)
The Affordable Care Act's requirement that certain individuals pay a
financial penalty for not obtaining health insurance may reasonably be
characterized as a tax. Because the Constitution permits such a tax,
it is not our role to forbid it, or to pass upon its wisdom or
fairness