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 $241.67   13.719%   $274.8247   $274.82   $274.80   $274.80  
  Purchase #2 $114.95   7.751%   $123.8598   $123.86   $123.85   $123.90  
  Purchase #3 $155.54   12.544%   $175.0509   $175.05   $175.05   $175.10  
  Purchase #4 $63.26   8.564%   $68.6776   $68.68   $68.70   $68.70  
  Purchase #5 $227.75   11.359%   $253.6201   $253.62   $253.60   $253.60  
  Purchase #6 $88.25   5.643%   $93.2299   $93.23   $93.25   $93.20  
  Purchase #7 $32.51   9.595%   $35.6293   $35.63   $35.65   $35.60  
  7 purchase totals = $923.93       $1,024.8923   $1,024.89   $1,024.90   $1,024.90