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 $182.30   8.874%   $198.4773   $198.48   $198.50   $198.50  
  Purchase #2 $84.72   12.859%   $95.6141   $95.61   $95.60   $95.60  
  Purchase #3 $55.48   6.289%   $58.9691   $58.97   $58.95   $59.00  
  Purchase #4 $240.62   4.709%   $251.9508   $251.95   $251.95   $252.00  
  Purchase #5 $178.36   7.464%   $191.6728   $191.67   $191.65   $191.70  
  Purchase #6 $169.78   8.116%   $183.5593   $183.56   $183.55   $183.60  
  Purchase #7 $227.66   13.413%   $258.196   $258.20   $258.20   $258.20  
  7 purchase totals = $1,138.92       $1,238.4394   $1,238.44   $1,238.40   $1,238.60