Still missing the point really. Tax codes are complex - our simple one* is a mere 5000** pages.
A multinational will have to comply with every such tax code, and no guarantee of consistency. Blaming companies for contrived tax affairs is a bit like blaming the cup cake for its shape.
1) Simple and consistent codes.
2) Profits should be taxed where economic activities deriving the profits are performed and where value is created. Now apply that to a software R&D lab (that's at least tax deductible anywhere in the world, often super tax deductible in the UK - not least as countries would rather be a locus for highly qualified, highly paid people who you know pay taxes) . The software is created in one place and profits and economic benefits of use elsewhere on either sale or use.
3) Ireland is not in the G20 and has a different approach to taxation - attract employment, tax employees.
Solve 1) , 2) and 3) simultaneously.
Anything that is not legally minimising taxation is by definition voluntary - and companies do a lot of voluntary and charity work and support around the world. CSR, 1%'ers whatever. Giving more money to taxation authorities is of course one of the worst ways to effectively achieve the desired objectives***. Nothing stops employees and shareholders doing the same , and again many do give to charities and more.
If you tax at a 'moral' rate then you have all sorts of non objective analysis on tax matters that will again by definition be discriminatory and imposing unpredictable judgements, further disincentivising investment.
Of course it can't be the G20 finance ministers fault, oh no must be those nasty companies that er provide most of the employment and tax revenues any way ...
*it must be , we have an Office of Tax Simplification and they say it is.
** after amending, redefining and dedupe, actually you may have to comply with up to 17,000 if you have any historical compliance.
*** according to Keynes