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 $230.43   13.394%   $261.2938   $261.29   $261.30   $261.30  
  Purchase #2 $248.34   7.122%   $266.0268   $266.03   $266.05   $266.00  
  Purchase #3 $69.81   8.569%   $75.792   $75.79   $75.80   $75.80  
  Purchase #4 $34.57   5.741%   $36.5547   $36.55   $36.55   $36.60  
  Purchase #5 $235.97   8.571%   $256.195   $256.20   $256.20   $256.20  
  Purchase #6 $64.64   7.828%   $69.7   $69.70   $69.70   $69.70  
  Purchase #7 $175.56   10.485%   $193.9675   $193.97   $193.95   $194.00  
  7 purchase totals = $1,059.32       $1,159.5298   $1,159.53   $1,159.55   $1,159.60