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 $217.99   13.768%   $248.0029   $248.00   $248.00   $248.00  
  Purchase #2 $151.93   4.786%   $159.2014   $159.20   $159.20   $159.20  
  Purchase #3 $232.49   3.601%   $240.862   $240.86   $240.85   $240.90  
  Purchase #4 $196.97   7.477%   $211.6974   $211.70   $211.70   $211.70  
  Purchase #5 $92.65   12.660%   $104.3795   $104.38   $104.40   $104.40  
  Purchase #6 $32.71   8.839%   $35.6012   $35.60   $35.60   $35.60  
  Purchase #7 $125.40   6.769%   $133.8883   $133.89   $133.90   $133.90  
  7 purchase totals = $1,050.14       $1,133.6327   $1,133.63   $1,133.65   $1,133.70