In places without any kind of unique ID, multiple voting is often prevented by dyeing your thumbnail after voting. This is sufficient to keep voter fraud down to insignificant levels. The UK commenter points out that a number specific to the voting process is also adequate to the purpose. Pension accounts can similarly be identified by numbers specific to the money in question, and in that case there's not even any requirement for being one to one—your pension contributions from different years can and possibly should be in separate, unlinked accounts. Certainly there is no benefit, and potentially enormous harm, in linking your pension to your voting.