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 $186.71   10.315%   $205.9691   $205.97   $205.95   $206.00  
  Purchase #2 $159.46   8.410%   $172.8706   $172.87   $172.85   $172.90  
  Purchase #3 $159.60   6.676%   $170.2549   $170.25   $170.25   $170.30  
  Purchase #4 $46.41   3.161%   $47.877   $47.88   $47.90   $47.90  
  Purchase #5 $240.98   3.275%   $248.8721   $248.87   $248.85   $248.90  
  Purchase #6 $76.81   8.274%   $83.1653   $83.17   $83.15   $83.20  
  Purchase #7 $143.98   7.360%   $154.5769   $154.58   $154.60   $154.60  
  7 purchase totals = $1,013.95       $1,083.5859   $1,083.59   $1,083.55   $1,083.80