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 $21.76   13.262%   $24.6458   $24.65   $24.65   $24.60  
  Purchase #2 $167.74   4.783%   $175.763   $175.76   $175.75   $175.80  
  Purchase #3 $186.26   12.151%   $208.8925   $208.89   $208.90   $208.90  
  Purchase #4 $235.97   6.316%   $250.8739   $250.87   $250.85   $250.90  
  Purchase #5 $16.87   10.464%   $18.6353   $18.64   $18.65   $18.60  
  Purchase #6 $95.99   8.112%   $103.7767   $103.78   $103.80   $103.80  
  Purchase #7 $143.41   6.419%   $152.6155   $152.62   $152.60   $152.60  
  7 purchase totals = $868.00       $935.2027   $935.21   $935.20   $935.20