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 $192.46   3.412%   $199.0267   $199.03   $199.05   $199.00  
  Purchase #2 $52.58   10.197%   $57.9416   $57.94   $57.95   $57.90  
  Purchase #3 $135.59   13.768%   $154.258   $154.26   $154.25   $154.30  
  Purchase #4 $100.85   6.526%   $107.4315   $107.43   $107.45   $107.40  
  Purchase #5 $238.29   9.852%   $261.7663   $261.77   $261.75   $261.80  
  Purchase #6 $9.54   13.214%   $10.8006   $10.80   $10.80   $10.80  
  Purchase #7 $133.92   4.708%   $140.225   $140.23   $140.25   $140.20  
  7 purchase totals = $863.23       $931.4497   $931.46   $931.50   $931.40