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 $242.38   6.179%   $257.3567   $257.36   $257.35   $257.40  
  Purchase #2 $239.63   9.252%   $261.8006   $261.80   $261.80   $261.80  
  Purchase #3 $161.69   7.645%   $174.0512   $174.05   $174.05   $174.10  
  Purchase #4 $68.91   9.216%   $75.2607   $75.26   $75.25   $75.30  
  Purchase #5 $152.87   6.417%   $162.6797   $162.68   $162.70   $162.70  
  Purchase #6 $169.53   13.845%   $193.0014   $193.00   $193.00   $193.00  
  Purchase #7 $14.94   13.681%   $16.9839   $16.98   $17.00   $17.00  
  7 purchase totals = $1,049.95       $1,141.1342   $1,141.13   $1,141.15   $1,141.30