conservatism: that's quite a technical one, so it's hard to find a good Latin equivalent. If one is happy with the statement of 'taking the lower value', pretium vilius might fit.
consistency: that means staying true to a choice made, so constantia or perseverantia would be a match.
materiality: that's again a very technical one, so again hard. I take it to mean that trifles can be ignored. A relatively direct translation might be gravitas, but that could also mean 'dignity'. Going more by the meaning, something like minimorum neglectio or pusillorum contemnatio might be a possibility.
full disclosure: there are a number of ways to say disclosure, but many of these have other meanings (publicatio can mean 'confiscation', which would be rather unfortunate for accountants, and ostentatio can mean 'vain display', which again would be against the spirit of accountancy), so I'd settle on declaratio plena.
There is a possible choice with the letter P in each case, so one could make the slogan alliterate as pretium vilius, perseverantia, pusillorum contemnatio, plena declaratio.