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 $62.50   4.781%   $65.4881   $65.49   $65.50   $65.50  
  Purchase #2 $247.76   4.807%   $259.6698   $259.67   $259.65   $259.70  
  Purchase #3 $103.67   3.623%   $107.426   $107.43   $107.45   $107.40  
  Purchase #4 $131.95   9.808%   $144.8917   $144.89   $144.90   $144.90  
  Purchase #5 $146.41   12.565%   $164.8064   $164.81   $164.80   $164.80  
  Purchase #6 $175.93   11.151%   $195.548   $195.55   $195.55   $195.50  
  Purchase #7 $84.40   8.701%   $91.7436   $91.74   $91.75   $91.70  
  7 purchase totals = $952.62       $1,029.5736   $1,029.58   $1,029.60   $1,029.50