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 $71.57   6.868%   $76.4854   $76.49   $76.50   $76.50  
  Purchase #2 $248.56   5.652%   $262.6086   $262.61   $262.60   $262.60  
  Purchase #3 $75.45   8.122%   $81.578   $81.58   $81.60   $81.60  
  Purchase #4 $91.47   7.664%   $98.4803   $98.48   $98.50   $98.50  
  Purchase #5 $24.44   13.322%   $27.6959   $27.70   $27.70   $27.70  
  Purchase #6 $247.26   12.241%   $277.5271   $277.53   $277.55   $277.50  
  Purchase #7 $96.62   8.872%   $105.1921   $105.19   $105.20   $105.20  
  7 purchase totals = $855.37       $929.5674   $929.58   $929.65   $929.60