Evitando código duplicado

ImpostoNotaFiscal_CodigoDuplicado.cs

public class ImpostosNotaFiscal
{
    public decimal CalcularValorLiquido(decimal valorNotaFiscal)
    {
        var impostoPis = CalcularPis(valorNotaFiscal);
        var impostoCofins = CalcularCofins(valorNotaFiscal);
        var impostoIrpj = CalcularIrpj(valorNotaFiscal);
        var impostoCsll = CalcularCsll(valorNotaFiscal);
        var impostos = impostoPis + impostoCofins + impostoIrpj + impostoCsll;
        return valorNotaFiscal - impostos;
    }

    public decimal CalcularImpostos(decimal valorNotaFiscal)
    {
        var impostoPis = CalcularPis(valorNotaFiscal);
        var impostoCofins = CalcularCofins(valorNotaFiscal);
        var impostoIrpj = CalcularIrpj(valorNotaFiscal);
        var impostoCsll = CalcularCsll(valorNotaFiscal);
        return impostoPis + impostoCofins + impostoIrpj + impostoCsll;
    }

    public decimal CalcularPis(decimal valorNotaFiscal)
    {
        var taxaImposto = 1.65M;
        return valorNotaFiscal * taxaImposto / 100;
    }

    public decimal CalcularCofins(decimal valorNotaFiscal)
    {
        var taxaImposto = 7.6M;
        return valorNotaFiscal * taxaImposto / 100;
    }

    public decimal CalcularIrpj(decimal valorNotaFiscal)
    {
        var taxaImposto = 15M;
        return valorNotaFiscal * taxaImposto / 100;
    }

    public decimal CalcularCsll(decimal valorNotaFiscal)
    {
        var taxaImposto = 9M;
        return valorNotaFiscal * taxaImposto / 100;
    }
}

ImpostoNotaFiscal_PrimeiroRound.cs

public class ImpostosNotaFiscal
{
    public decimal CalcularValorLiquido(decimal valorNotaFiscal)
    {
        return valorNotaFiscal - CalcularImpostos(valorNotaFiscal);
    }

    public decimal CalcularImpostos(decimal valorNotaFiscal)
    {
        var impostoPis = CalcularPis(valorNotaFiscal);
        var impostoCofins = CalcularCofins(valorNotaFiscal);
        var impostoIrpj = CalcularIrpj(valorNotaFiscal);
        var impostoCsll = CalcularCsll(valorNotaFiscal);
        return impostoPis + impostoCofins + impostoIrpj + impostoCsll;
    }

    public decimal CalcularPis(decimal valorNotaFiscal)
    {
        var taxaImposto = 1.65M;
        return valorNotaFiscal * taxaImposto / 100;
    }

    public decimal CalcularCofins(decimal valorNotaFiscal)
    {
        var taxaImposto = 7.6M;
        return valorNotaFiscal * taxaImposto / 100;
    }

    public decimal CalcularIrpj(decimal valorNotaFiscal)
    {
        var taxaImposto = 15M;
        return valorNotaFiscal * taxaImposto / 100;
    }

    public decimal CalcularCsll(decimal valorNotaFiscal)
    {
        var taxaImposto = 9M;
        return valorNotaFiscal * taxaImposto / 100;
    }
}

ImpostoNotaFiscal_SegundoRound.cs

public class ImpostosNotaFiscal
{
    public decimal CalcularValorLiquido(decimal valorNotaFiscal)
    {
        return valorNotaFiscal - CalcularImpostos(valorNotaFiscal);
    }

    public decimal CalcularImpostos(decimal valorNotaFiscal)
    {
        var impostoPis = CalcularPis(valorNotaFiscal);
        var impostoCofins = CalcularCofins(valorNotaFiscal);
        var impostoIrpj = CalcularIrpj(valorNotaFiscal);
        var impostoCsll = CalcularCsll(valorNotaFiscal);
        return impostoPis + impostoCofins + impostoIrpj + impostoCsll;
    }

    public decimal CalcularPis(decimal valorNotaFiscal)
    {
        return CalcularImposto(valorNotaFiscal, 1.65M);
    }

    public decimal CalcularCofins(decimal valorNotaFiscal)
    {
        return CalcularImposto(valorNotaFiscal, 7.6M);
    }

    public decimal CalcularIrpj(decimal valorNotaFiscal)
    {
        return CalcularImposto(valorNotaFiscal, 15M);
    }

    public decimal CalcularCsll(decimal valorNotaFiscal)
    {
        return CalcularImposto(valorNotaFiscal, 9M);
    }

    public decimal CalcularImposto(decimal valorNotaFiscal, decimal taxaImposto)
    {
        return valorNotaFiscal * taxaImposto / 100;
    }
}

ImpostoNotaFiscal_TerceiroRound.cs

public class ImpostosNotaFiscal
{
    public decimal CalcularValorLiquido(decimal valorNotaFiscal)
        => valorNotaFiscal - CalcularImpostos(valorNotaFiscal);

    public decimal CalcularImpostos(decimal valorNotaFiscal)
    {
        var impostoPis = CalcularPis(valorNotaFiscal);
        var impostoCofins = CalcularCofins(valorNotaFiscal);
        var impostoIrpj = CalcularIrpj(valorNotaFiscal);
        var impostoCsll = CalcularCsll(valorNotaFiscal);
        return impostoPis + impostoCofins + impostoIrpj + impostoCsll;
    }

    public decimal CalcularPis(decimal valorNotaFiscal)
        => CalcularImposto(valorNotaFiscal, 1.65M);

    public decimal CalcularCofins(decimal valorNotaFiscal)
        => CalcularImposto(valorNotaFiscal, 7.6M);

    public decimal CalcularIrpj(decimal valorNotaFiscal)
        => CalcularImposto(valorNotaFiscal, 15M);

    public decimal CalcularCsll(decimal valorNotaFiscal)
        => CalcularImposto(valorNotaFiscal, 9M);

    public decimal CalcularImposto(decimal valorNotaFiscal, decimal taxaImposto)
        => valorNotaFiscal * taxaImposto / 100;
}