From the Regional Economic Report (IER) 2016-2017: Opportunities and challenges for Central America, by the SIECA:
 
Size of the tax burden in Central America increases 

In terms of income, the tax burden increased in all of the countries in the region, although in none of them, at least in the period under study, was any tax reform implemented from which the marginal tax increases are derived. 

The collection figures show that the tax burden of the isthmus went from 13.4% in 2014 to 13.6% in 2015 and to 14.0% in 2016, due to both the lagged effects of the tax reforms in Honduras and Nicaragua, as well as recovery efforts in the institutional framework of the tax administrations in Guatemala and Panama. Also playing a part are administrative improvements and strengthening of controls that were implemented in El Salvador and Costa Rica, in order to have a higher level of fiscal resources.  

Read full report "Regional Economic Report 2016/17: Challenges and opportunities in Central America" (in spanish).

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Fiscal Outlook in Central America

February 2018

In one of the regions that receives the least amount of taxes in the world, the tax burden remained relatively stable in 2017.

From the section Fiscal Outlook for Central America, from the report "Macro-fiscal Profiles: 9th edition", by the Central American Institute of Fiscal Studies (Icefi):

A New Fiscal Agenda for Guatemala

January 2016

In the opinion of the Central American Institute of Fiscal Studies, the only way to consolidate public finances in a sustainable way is to reduce tax breaks and increase tax collections.

From a statement issued by the Central Institute for Fiscal Studies (Icefi):

The Central American Institute for Fiscal Studies (Icefi) has proposed as a fiscal agenda for development: meeting the public demand for integrity and transparency; effective, efficient and effectual public spending as a tool for inclusive and democratic development; and financial viability with taxation being part of democratic accountability.

Fiscal Accounts in Central America

November 2014

The average tax burden for the region is 13.4% of GDP, while the average public expenditure increased from 18.7% in 2013 to 19.2% at the end of 2014.

From the Introduction of the report Macrofiscal profiles in Central America, from Instituto Centroamericano de Estudios Fiscales (Icefi):

Guatemala's Financial Present and Future

July 2014

A review of the fiscal outlook in Guatemala, the difficulties encountered and possible solutions for addressing these challenges.

From the Introduction of the study by the Foundation for the Development of Guatemala (FUNDESA):

In any country, taxation is critical to ensuring the proper functioning of the state.