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 $51.69   6.770%   $55.1894   $55.19   $55.20   $55.20  
  Purchase #2 $215.66   11.669%   $240.8254   $240.83   $240.85   $240.80  
  Purchase #3 $250.69   4.703%   $262.48   $262.48   $262.50   $262.50  
  Purchase #4 $197.38   8.779%   $214.708   $214.71   $214.70   $214.70  
  Purchase #5 $166.78   12.758%   $188.0578   $188.06   $188.05   $188.10  
  Purchase #6 $206.29   5.145%   $216.9036   $216.90   $216.90   $216.90  
  Purchase #7 $186.32   5.241%   $196.085   $196.09   $196.10   $196.10  
  7 purchase totals = $1,274.81       $1,374.2492   $1,374.26   $1,374.30   $1,374.30