Per the IRS Instructions for Form 8949, page 5:
Stock acquired on various dates. If you sold a block of stock (or similar property) that was acquired through several different purchases, you may report the sale on one row and enter "VARIOUS" in column (b). However, you still must report the short-term gain or (loss) on the sale on Part I, and the long-term gain or (loss) on Part II.
TaxAct® supports an entry of "VARIOUS" as the date acquired on Form 1099-B. You would enter the data on Form 1099-B in the Investment Income section of TaxAct. Enter "Various" for date acquired, then enter the cost basis, date sold, and sales proceeds. The holding period will be determined based upon the reporting category you select (A-C for short-term; D-F for long-term), if one has already been selected. However, if a reporting category has not already been selected, the program will default to reporting category A, indicating a short-term transaction.
To enter this information in your TaxAct return: