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 $226.33   13.636%   $257.1924   $257.19   $257.20   $257.20  
  Purchase #2 $134.59   8.657%   $146.2415   $146.24   $146.25   $146.20  
  Purchase #3 $169.32   6.681%   $180.6323   $180.63   $180.65   $180.60  
  Purchase #4 $191.30   8.719%   $207.9794   $207.98   $208.00   $208.00  
  Purchase #5 $32.91   8.242%   $35.6224   $35.62   $35.60   $35.60  
  Purchase #6 $111.67   8.696%   $121.3808   $121.38   $121.40   $121.40  
  Purchase #7 $35.83   4.295%   $37.3689   $37.37   $37.35   $37.40  
  7 purchase totals = $901.95       $986.4177   $986.41   $986.45   $986.40