You can enter it all in spreadsheet and upload the data into a line graph plotting sales volume as Y and date in time as X. That will give you a view of your sales trends, just match it based on month and season. You can also watch to see how the overall economy has affected your sales. See if there's a change in 2007 for example. You also find other graphs based on industry or public companies to compare your trends to the industry.
Analysis is easy without fancy software. Based on the high times, you would plan your business around that. Especially if you notice a drop in your competition, thats the perfect time to boosts advertising and sales efforts. I'm a small business planning consultant with a commercial bank and a small funding company. I use this simple method to make recommendations to clients to leverage a line of credit during peak sales times to buy additional inventory to sell, or materials to manufacture. Also use it to time loan payments. For example a commercial fishery is only busy during nov through April, we would plan a bi annual loan repayment based those times when the business has money instead a month to month and potentially causing cash flow problems. Knowing these kinds of things really helps establish a real plan, and helps with what I call your "exit strategy" (aka your retirement plan, desire to build and grow, or desire to build and sell)
Software that makes recommendations and analysis reports are generally overly expensive
Depending on your industry and what you are looking to uncover and plan for, I really don't mind helping. Feel free to email me sometime. firstname.lastname@example.org.
Experience as a Small Business Lender and Area Manager, owner of a small funding company.