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 $225.39   12.226%   $252.9462   $252.95   $252.95   $252.90  
  Purchase #2 $250.80   4.173%   $261.2659   $261.27   $261.25   $261.30  
  Purchase #3 $112.34   10.811%   $124.4851   $124.49   $124.50   $124.50  
  Purchase #4 $242.95   6.317%   $258.2972   $258.30   $258.30   $258.30  
  Purchase #5 $168.64   5.501%   $177.9169   $177.92   $177.90   $177.90  
  Purchase #6 $110.86   12.474%   $124.6887   $124.69   $124.70   $124.70  
  Purchase #7 $92.50   10.621%   $102.3244   $102.32   $102.30   $102.30  
  7 purchase totals = $1,203.48       $1,301.9244   $1,301.94   $1,301.90   $1,301.90