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 $114.73   6.602%   $122.3045   $122.30   $122.30   $122.30  
  Purchase #2 $42.26   11.834%   $47.261   $47.26   $47.25   $47.30  
  Purchase #3 $55.51   7.272%   $59.5467   $59.55   $59.55   $59.50  
  Purchase #4 $229.36   8.594%   $249.0712   $249.07   $249.05   $249.10  
  Purchase #5 $233.42   11.870%   $261.127   $261.13   $261.15   $261.10  
  Purchase #6 $157.71   8.338%   $170.8599   $170.86   $170.85   $170.90  
  Purchase #7 $125.62   4.115%   $130.7893   $130.79   $130.80   $130.80  
  7 purchase totals = $958.61       $1,040.9596   $1,040.96   $1,040.95   $1,041.00