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 $76.94   6.482%   $81.9273   $81.93   $81.95   $81.90  
  Purchase #2 $81.32   5.300%   $85.63   $85.63   $85.65   $85.60  
  Purchase #3 $119.60   5.328%   $125.9723   $125.97   $125.95   $126.00  
  Purchase #4 $102.64   8.348%   $111.2084   $111.21   $111.20   $111.20  
  Purchase #5 $136.69   4.636%   $143.0269   $143.03   $143.05   $143.00  
  Purchase #6 $242.39   7.291%   $260.0627   $260.06   $260.05   $260.10  
  Purchase #7 $65.65   11.772%   $73.3783   $73.38   $73.40   $73.40  
  7 purchase totals = $825.23       $881.2059   $881.21   $881.25   $881.20