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 $131.76   6.600%   $140.4562   $140.46   $140.45   $140.50  
  Purchase #2 $208.71   12.354%   $234.494   $234.49   $234.50   $234.50  
  Purchase #3 $196.42   9.183%   $214.4572   $214.46   $214.45   $214.50  
  Purchase #4 $11.58   8.510%   $12.5655   $12.57   $12.55   $12.60  
  Purchase #5 $67.33   8.669%   $73.1668   $73.17   $73.15   $73.20  
  Purchase #6 $39.77   5.803%   $42.0779   $42.08   $42.10   $42.10  
  Purchase #7 $130.94   13.526%   $148.6509   $148.65   $148.65   $148.70  
  7 purchase totals = $786.51       $865.8685   $865.88   $865.85   $866.10