Decimal places usually are a contraints given by the exchange, and it's not something you can choose.
Fee displayed by CAT are only an "info", but fees calculated are correct and directly obtained by the API CALL.

FROM KRAKEN DOCUMENTATION :

Get open positions
URL: https://api.kraken.com/0/private/OpenPositions

Input:

txid = comma delimited list of transaction ids to restrict output to
docalcs = whether or not to include profit/loss calculations (optional.  default = false)
Result: associative array of open position info

= open position info
    ordertxid = order responsible for execution of trade
    pair = asset pair
    time = unix timestamp of trade
    type = type of order used to open position (buy/sell)
    ordertype = order type used to open position
    cost = opening cost of position (quote currency unless viqc set in oflags)
    fee = opening fee of position (quote currency)
    vol = position volume (base currency unless viqc set in oflags)
    vol_closed = position volume closed (base currency unless viqc set in oflags)
    margin = initial margin (quote currency)
    value = current value of remaining position (if docalcs requested.  quote currency)
    net = unrealized profit/loss of remaining position (if docalcs requested.  quote currency, quote currency scale)
    misc = comma delimited list of miscellaneous info
    oflags = comma delimited list of order flags
        viqc = volume in quote currency