fix: POS consolidated invoice rounded total issue

[nemesis189]

Ref issue: ISS-21-22-06296

Problem:
Consider the following 2 POS Invoices:

invoice 1:

Invoice 2:

Consolidated Invoice of the above two:

• The total gets rounded in both the invoices and 0.50 is deducted from the total of both invoices
• So the effect totals and the amount paid in both the invoices now are: 250 and 50
• On consolidating these 2 invoices, the total becomes:
  250.5 + 50.5 = 301
• The effective amount actually paid is 250+50 = 300, since the totals of individual invoices were rounded off
• In the consolidated invoice, the paid amount is calculated by adding paid amounts from individual pos invoices
• The amount to be paid in the consolidated sales invoice gets recalculated as 301 after merging the two POS invoices
• Since only 300 was paid and the sales invoice has 301 as the amount to be paid, the consolidated invoice would remain in unpaid state and there would be an outstanding amount of Re. 1

Solution:

Fixed Consolidated Invoice of the above two:

• Adding the Rounding Adjustment and Rounded Total of the individual POS invoices while merging to calculate the same for Consolidated Invoice
• In calculate_taxes method, rounding adjustment was being overriden so bypassed that for consolidated invoices
• In calculate_totals method, total_taxes_and_charges was being calculated even when there were no taxes applied, so added a condition for the same

[codecov]

Codecov Report

Merging #28006 (b5b0039) into develop (7acdcc7) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop   #28006      +/-   ##
===========================================
- Coverage    54.43%   54.41%   -0.03%     
===========================================
  Files         1254     1255       +1     
  Lines        67717    67838     +121     
===========================================
+ Hits         36861    36911      +50     
- Misses       30856    30927      +71     

Impacted Files	Coverage Δ
...ype/pos_invoice_merge_log/pos_invoice_merge_log.py	75.65% <100.00%> (+0.94%)	⬆️
erpnext/controllers/taxes_and_totals.py	97.63% <100.00%> (+0.02%)	⬆️
...ctype/product_tax_category/product_tax_category.py	0.00% <0.00%> (-100.00%)	⬇️
...rations/doctype/taxjar_settings/taxjar_settings.py	29.50% <0.00%> (-70.50%)	⬇️
...ctype/woocommerce_settings/woocommerce_settings.py	80.39% <0.00%> (-3.93%)	⬇️
...e/asset_value_adjustment/asset_value_adjustment.py	87.80% <0.00%> (-3.66%)	⬇️
...eport/item_variant_details/item_variant_details.py	84.52% <0.00%> (-3.58%)	⬇️
erpnext/shopping_cart/utils.py	32.14% <0.00%> (-3.58%)	⬇️
...wise_balance_history/batch_wise_balance_history.py	91.52% <0.00%> (-1.70%)	⬇️
erpnext/stock/report/stock_ledger/stock_ledger.py	78.33% <0.00%> (-1.67%)	⬇️
... and 35 more

[nextchamp-saqib]

@Mergifyio backport version-13-hotfix

[mergify]

backport version-13-hotfix

✅ Backports have been created

• #28146 fix: POS consolidated invoice rounded total issue (backport #28006) has been created for branch version-13-hotfix