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 $38.81   8.856%   $42.247   $42.25   $42.25   $42.20  
  Purchase #2 $197.34   9.128%   $215.3532   $215.35   $215.35   $215.40  
  Purchase #3 $45.76   8.623%   $49.7059   $49.71   $49.70   $49.70  
  Purchase #4 $215.55   5.537%   $227.485   $227.49   $227.50   $227.50  
  Purchase #5 $47.88   9.329%   $52.3467   $52.35   $52.35   $52.30  
  Purchase #6 $235.42   6.176%   $249.9595   $249.96   $249.95   $250.00  
  Purchase #7 $224.76   6.813%   $240.0729   $240.07   $240.05   $240.10  
  7 purchase totals = $1,005.52       $1,077.1702   $1,077.18   $1,077.15   $1,077.20