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 $188.62   5.260%   $198.5414   $198.54   $198.55   $198.50  
  Purchase #2 $241.46   8.694%   $262.4525   $262.45   $262.45   $262.50  
  Purchase #3 $173.47   13.396%   $196.708   $196.71   $196.70   $196.70  
  Purchase #4 $190.53   6.860%   $203.6004   $203.60   $203.60   $203.60  
  Purchase #5 $242.29   3.266%   $250.2032   $250.20   $250.20   $250.20  
  Purchase #6 $49.65   12.786%   $55.9982   $56.00   $56.00   $56.00  
  Purchase #7 $187.43   5.306%   $197.375   $197.38   $197.40   $197.40  
  7 purchase totals = $1,273.45       $1,364.8787   $1,364.88   $1,364.90   $1,364.90