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 $57.82   10.535%   $63.9113   $63.91   $63.90   $63.90  
  Purchase #2 $199.57   3.553%   $206.6607   $206.66   $206.65   $206.70  
  Purchase #3 $217.78   3.238%   $224.8317   $224.83   $224.85   $224.80  
  Purchase #4 $102.41   9.803%   $112.4493   $112.45   $112.45   $112.40  
  Purchase #5 $239.69   10.696%   $265.3272   $265.33   $265.35   $265.30  
  Purchase #6 $41.35   4.732%   $43.3067   $43.31   $43.30   $43.30  
  Purchase #7 $24.58   8.508%   $26.6713   $26.67   $26.65   $26.70  
  7 purchase totals = $883.20       $943.1582   $943.16   $943.15   $943.10