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 $65.63   11.835%   $73.3973   $73.40   $73.40   $73.40  
  Purchase #2 $98.58   4.827%   $103.3385   $103.34   $103.35   $103.30  
  Purchase #3 $90.47   6.191%   $96.071   $96.07   $96.05   $96.10  
  Purchase #4 $199.66   12.796%   $225.2085   $225.21   $225.20   $225.20  
  Purchase #5 $14.25   11.611%   $15.9046   $15.90   $15.90   $15.90  
  Purchase #6 $85.30   8.182%   $92.2792   $92.28   $92.30   $92.30  
  Purchase #7 $18.28   8.682%   $19.8671   $19.87   $19.85   $19.90  
  7 purchase totals = $572.17       $626.0662   $626.07   $626.05   $626.10