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 $63.61   8.423%   $68.9679   $68.97   $68.95   $69.00  
  Purchase #2 $121.44   12.379%   $136.4731   $136.47   $136.45   $136.50  
  Purchase #3 $235.66   4.730%   $246.8067   $246.81   $246.80   $246.80  
  Purchase #4 $29.95   12.635%   $33.7342   $33.73   $33.75   $33.70  
  Purchase #5 $164.66   13.347%   $186.6372   $186.64   $186.65   $186.60  
  Purchase #6 $70.43   3.387%   $72.8155   $72.82   $72.80   $72.80  
  Purchase #7 $11.39   12.512%   $12.8151   $12.82   $12.80   $12.80  
  7 purchase totals = $697.14       $758.2497   $758.26   $758.20   $758.20