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Generic ceramic capacitors are for a generic voltage rating which I personally take as 50V for these sized caps. I won't use them on anything above (say) 20-25V.
Most of the time I prefer surface mount caps even for prototypes (they can still be used on stripboard, just solder on the underside). It is very cheap to buy surface mount 100nF and 10nF and 220nf capacitors (as an example) in quantities of (say) 50 for just a couple of dollars, and then you know their rating for definite, and will last you for ages.
EDIT: Please note if you don't know the specification of a tantalum cap (or electrolytic) but use it anyway, there is a high risk they will explode or burst respectively.