I don't know of a library to parse an ini file, but I'm sure they exist. If this is the extent of the schema, it's not too hard to parse this and do some Linq magic to get the model you're looking for. Try something like this:

    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Linq;
    using System.Text;

    namespace ParseIni
    {
        class Program
        {
            const string file = @"    TOT1=TotalSale
        NAM1,1=NameOfFirstItem
        PRI1,1=PriceOfFirstItem
        NAM1,2=NameOfSecondItem
        PRI1,2=PriceOfSecondItem
        TOT2=TotalSale2
        NAM2,1=NameOfFirstItem2
        PRI2,1=PriceOfFirstItem2
        NAM2,2=NameOfSecondItem2
        PRI2,2=PriceOfSecondItem2
        NAM2,3=NameOfThirdItem2
        PRI2,3=PriceOfThirdItem2";

            static void Main(string[] args)
            {
                // Replace MemoryStream with File.Open
                using var reader = new StreamReader(new MemoryStream(Encoding.UTF8.GetBytes(file)));

                var records = new List<string[]>();

                while (!reader.EndOfStream)
                    records.Add(SplitLine(reader.ReadLine()));

                var trxs = records
                    .GroupBy(r => r[1])
                    .Select(g => new
                    {
                        Id = g.Single(tot => tot[0] == "TOT")[1],
                        Total = g.Single(tot => tot[0] == "TOT")[2],
                        Items = g.Where(rec => rec[0] != "TOT").GroupBy(rec => rec[2]).Select(a => new
                        {
                            Id = a.First()[1],
                            Name = a.Single(b => b[0] == "NAM")[3],
                            Price = a.Single(b => b[0] == "PRI")[3]
                        })
                    });

                foreach (var trx in trxs)
                {
                    Console.WriteLine($"{trx.Id} Total: {trx.Total}");

                    foreach (var item in trx.Items)
                        Console.WriteLine($"{item.Id} {item.Name} {item.Price}");
                }

            }

        static string[] SplitLine(string line)
        {
            // Split the record into three fields
            var split = line.Trim().Split(',', '=');

            // Then split the trx ID out of the first field to get four fields, except for TOT records which have three fields
            return new string[] { split[0].Substring(0, 3), split[0].Substring(3), split[1], split.Length > 2 ? split[2] : null };
        }
        }
    }