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 $249.68   9.232%   $272.7305   $272.73   $272.75   $272.70  
  Purchase #2 $117.39   12.174%   $131.6811   $131.68   $131.70   $131.70  
  Purchase #3 $119.69   6.828%   $127.8624   $127.86   $127.85   $127.90  
  Purchase #4 $21.45   5.189%   $22.563   $22.56   $22.55   $22.60  
  Purchase #5 $175.55   9.179%   $191.6637   $191.66   $191.65   $191.70  
  Purchase #6 $45.81   6.713%   $48.8852   $48.89   $48.90   $48.90  
  Purchase #7 $142.90   12.392%   $160.6082   $160.61   $160.60   $160.60  
  7 purchase totals = $872.47       $955.9941   $955.99   $956.00   $956.10