Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $200.49   7.187%   $214.8992   $214.90   $214.90   $214.90  
  Purchase #2 $61.56   4.856%   $64.5494   $64.55   $64.55   $64.50  
  Purchase #3 $118.59   5.205%   $124.7626   $124.76   $124.75   $124.80  
  Purchase #4 $43.96   6.812%   $46.9546   $46.95   $46.95   $47.00  
  Purchase #5 $201.45   13.796%   $229.242   $229.24   $229.25   $229.20  
  Purchase #6 $158.58   11.853%   $177.3765   $177.38   $177.40   $177.40  
  Purchase #7 $170.70   6.783%   $182.2786   $182.28   $182.30   $182.30  
  7 purchase totals = $955.33       $1,040.0629   $1,040.06   $1,040.10   $1,040.10