2019 for 2016 in subparagraph (A)(ii) thereof. If any increase determined under this paragraph is not a multiple of $100, such increase shall be rounded to the next highest multiple of $100. . (e) Conforming amendment Section 1324(b)(2) of title 31, United States Code, is amended by inserting 21 (by reason of subsection (g) thereof), before 25A . (f) Coordination with possession tax systems Section 21(g)(1) of the Internal Revenue Code of 1986 (as added by this section) shall not apply to any person— (1) to whom a credit is allowed against taxes imposed by a possession with a mirror code tax system by reason of the application of section 21 of such Code in such possession for such taxable year, or (2) to whom a credit would be allowed against taxes imposed by a possession which does not have a mirror code tax system if the provisions of section 21 of such Code had been in effect in such possession for such taxable year. (g) Effective date The amendments made by this section shall apply to taxable years beginning after December 31, 2019. 403. Increase in exclusion for employer-provided dependent care assistance (a) In general Section 129(a)(2)(A) of the Internal Revenue Code of 1986 is amended by striking $5,000 ($2,500 and inserting $10,500 (half such dollar amount . (b) Inflation adjustment Section 129(a)(2) is amended by adding at the end the following new subparagraph: (D) Inflation adjustment In the case of any taxable year beginning after December 31, 2020, the $10,500 amount in subparagraph (A) shall be increased by an amount equal to— (i) such dollar amount, multiplied by (ii) the cost-of-living adjustment determined under section 1(f)(3) for the calendar year in which the taxable year begins, determined by substituting 2019 for 2016 in subparagraph (A)(ii) thereof. Any increase determined under the preceding sentence which is not a multiple of $50, shall be rounded to the next highest multiple of $50. . (c) Effective date The amendment made by this section shall apply to taxable years beginning after