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 $56.63   3.177%   $58.4291   $58.43   $58.45   $58.40  
  Purchase #2 $49.70   13.799%   $56.5581   $56.56   $56.55   $56.60  
  Purchase #3 $155.37   3.783%   $161.2476   $161.25   $161.25   $161.20  
  Purchase #4 $250.63   4.795%   $262.6477   $262.65   $262.65   $262.60  
  Purchase #5 $228.49   13.320%   $258.9249   $258.92   $258.90   $258.90  
  Purchase #6 $238.81   10.744%   $264.4677   $264.47   $264.45   $264.50  
  Purchase #7 $63.88   10.321%   $70.4731   $70.47   $70.45   $70.50  
  7 purchase totals = $1,043.51       $1,132.7482   $1,132.75   $1,132.70   $1,132.70