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 $232.73   13.542%   $264.2463   $264.25   $264.25   $264.20  
  Purchase #2 $179.46   6.767%   $191.6041   $191.60   $191.60   $191.60  
  Purchase #3 $21.93   3.624%   $22.7247   $22.72   $22.70   $22.70  
  Purchase #4 $53.76   9.652%   $58.9489   $58.95   $58.95   $58.90  
  Purchase #5 $168.41   8.662%   $182.9977   $183.00   $183.00   $183.00  
  Purchase #6 $184.93   4.759%   $193.7308   $193.73   $193.75   $193.70  
  Purchase #7 $227.75   9.568%   $249.5411   $249.54   $249.55   $249.50  
  7 purchase totals = $1,068.97       $1,163.7936   $1,163.79   $1,163.80   $1,163.60