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 $103.94   9.872%   $114.201   $114.20   $114.20   $114.20  
  Purchase #2 $59.76   3.523%   $61.8653   $61.87   $61.85   $61.90  
  Purchase #3 $241.54   6.460%   $257.1435   $257.14   $257.15   $257.10  
  Purchase #4 $250.62   4.526%   $261.9631   $261.96   $261.95   $262.00  
  Purchase #5 $27.66   5.570%   $29.2007   $29.20   $29.20   $29.20  
  Purchase #6 $169.91   7.486%   $182.6295   $182.63   $182.65   $182.60  
  Purchase #7 $78.47   11.561%   $87.5419   $87.54   $87.55   $87.50  
  7 purchase totals = $931.90       $994.5450   $994.54   $994.55   $994.50