Did you try to set the measured field meta to include "decimals" => 2 like this:

->pipe(new Pivot(...))
->pipe(new \koolreport\processes\ColumnMeta([
    "sales - sum" => [ // a measured field name format is "{field} - {operator}"
        "type" => "number",
        "decimals" => 2,
    ],
    "sales - count" => [ 
        "type" => "number",
        "decimals" => 2,
    ],
]))
->pipe($this->dataStore(...));