Regardless of what interface you choose, you will need all the sales info in
the one table.

There is no problem with entering the same date on several rows, for several
stores.

If you want the date text box to default to today, just set its Default
Value property to:
   =Date()

What salad said .. and a simple way of limiting to just the one date is to
create a form with no recordsource and on it put a control for entering the
date you want to view or edit.  Then add a sub-form - the sub-form record
source would be the sales table.  The sub-form control properties would be

Link Child Fields = SalesDate
Link Master Fields = controlDateOnMainForm

Now only the records with that date show, and any added records default to
that date.  This form design is easy and assumes you really only want to
enter / show records for one date at a time ;-)

If you want you can add a command button that adds runs an append query to
add a new record for each store with the date set to the date on
controlDateOnMainForm - this way you can just fill in the values for each
store and won't have to wonder if you missed any stores.  If a store had no
sales you would delete that stores sales record.

Roger

I, for the most part, ALWAYS have an autonumber field as my primary key.
 It makes life less complicated.  For example, in the BeforeUpdate
event I might want to check if something exists.  Ex:
    If Me.NewRecord then
        Dim var As Variant
        var = Dlookup("ID","TableName","StoreID = " & _
            Me.StoreID & " And ID <> " & Me.ID)
        If Not IsNull(var) Then
            msgbox "This store record already exists"
            Cancel = True
        Endif
    Endif

Now, the above is a bit unnecessary but sometimes you want to check for
a record that contains the same info but the AUTONUMBER does not match
the current autonumber field.

Your situation is a classic example for a form/subform.  In this
instance I might have an unbound form...it really depends on how you set
up your tables.  In the main form, I might have a combo box that lists
all of your stores with 2 columns; StoreID and StoreName.  In a textbox
I'd have the date field.  In the AfterUpdate event for the combo box,
and date text box, and perhaps the OnCurrent or OnLoad events I'd have
some code like
    SetFilter

Next, I'd have a subform that would list the data for the store/date
selected in the main form.  It would have no filter.

Now drop the subform into the main form.

Let's say the main form is called MainForm and the subform is called
SubForm.  Your SetFilter code may look something like this...
    Private Sub SetFilter
        Forms!MainForm!SubForm.Form.Filter = _
            "StoreID = " & Me.ComboStoreID & " And " & _
            "StoreDate = #" & Me.InputDateField & "#"
        Forms!MainForm!SubForm.Form.FilterOn = True

You can shorten the references like this
    Me("SubForm").Form.FilterOn = True

Of course, if the main table was bound to a table that stored the
StoreID and Date and the subform contained date related to it, the
form/Subform could be linked with the Master/Child relationship.