Fix negatives in journal entries totals

[dvdl16]

Description

fix: set tax_amount to have same sign as incl_tax_amount

Type of change

• 🟢 Bug fix (change which fixes an issue)
• ⚪ New feature (change which adds functionality)
• ⚪ Breaking change (fix or feature that would cause existing functionality to not work as expected)

Tests

• [x] Unit Tests have been updated or added, as required
• [ ] UI Tests have been updated or added, as required

Checklist:

• [x] My code follows Naming Guidelines (DocType, Field and Variable naming)
• [x] No Form changes / My code follows the Form Design Guidelines
• [x] My code follows the Coding Standards of this project
• [x] My code follows the Code Security Guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas / No comments necessary
• [ ] I have made corresponding additions/changes to the documentation
• [x] All business logic and validations are on the server-side / No business logic or validation changes
• [x] No patches are necessary / Migration Patches have been added to the correct subdirectory of /patches and patches.txt have been updated

User Experience:

N/A

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 63.40%. Comparing base (16bfe81) to head (9b225c5). Report is 1 commits behind head on version-15.

Files	Patch %	Lines
csf_za/__init__.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## version-15 #10 +/- ## ============================================== + Coverage 62.23% 63.40% +1.16% ============================================== Files 8 8 Lines 188 194 +6 ============================================== + Hits 117 123 +6 Misses 71 71 ```

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