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 $73.83   3.518%   $76.4273   $76.43   $76.45   $76.40  
  Purchase #2 $133.58   3.554%   $138.3274   $138.33   $138.35   $138.30  
  Purchase #3 $105.70   6.272%   $112.3295   $112.33   $112.35   $112.30  
  Purchase #4 $69.55   11.333%   $77.4321   $77.43   $77.45   $77.40  
  Purchase #5 $133.31   6.115%   $141.4619   $141.46   $141.45   $141.50  
  Purchase #6 $228.72   8.720%   $248.6644   $248.66   $248.65   $248.70  
  Purchase #7 $248.63   9.858%   $273.1399   $273.14   $273.15   $273.10  
  7 purchase totals = $993.32       $1,067.7825   $1,067.78   $1,067.85   $1,067.70