[CRM-20772] Price set calculation precision when sales tax enabled - CiviCRM Issue Tracker

Details

Type: Bug
Status: Done/Fixed
Priority: Minor
Resolution: Unresolved
Affects Version/s: 4.7.21, 4.7.20
Fix Version/s: None
Component/s: CiviContribute
Labels:
- PatchSubmitted

Versioning Impact:
Patch (backwards-compatible bug fixes)
Documentation Required?:
None
Funding Source:
Contributed Code
Verified?:
No
How it works currently:
Text quantity fields get calculated with additional pence. It's not possible to specify an exact amount as the sales TAX is calculated on top of the amount. Example: 16.67 + 20% tax = 20.004. 2x this = 40.01
How it should work:

Hide
Text quantity fields get calculated with additional pence. It's not possible to specify an exact amount as the sales TAX is calculated on top of the amount. Example: 16.666666 + 20% tax = 20.004.
When multiplying together, round to 2 decimal places first: 2x 20.00 = 40.00

Show
Text quantity fields get calculated with additional pence. It's not possible to specify an exact amount as the sales TAX is calculated on top of the amount. Example: 16.666666 + 20% tax = 20.004. When multiplying together, round to 2 decimal places first: 2x 20.00 = 40.00

Description

When sales tax is enabled price set calculations for text/numeric quantity generate amounts including the odd penny.

For example (create this as a price set and use the preview form):

Text quantity: 16.67. Inc VAT = 20.00. When you add two of these the total amount=40.01

Following discussion on mattermost, the sensible way to fix this is to allow multiple decimals to be entered in the pre-salestax amount. For the example above:

Text quantity: 16.6666666. Inc VAT = 20.00. When you add two of these the total amount=40.00.

This patch additionally replaces the generic "sales tax" text with the actual tax term (eg. VAT) in the UI.

It also requires a database column change in civicrm_membership_type to avoid a loss of precision - varchar(512) seems like a rather large column but that is what is set in civicrm_contribution.