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 $241.89   12.561%   $272.2738   $272.27   $272.25   $272.30  
  Purchase #2 $192.40   3.277%   $198.7049   $198.70   $198.70   $198.70  
  Purchase #3 $157.59   11.726%   $176.069   $176.07   $176.05   $176.10  
  Purchase #4 $148.67   13.322%   $168.4758   $168.48   $168.50   $168.50  
  Purchase #5 $42.57   10.788%   $47.1625   $47.16   $47.15   $47.20  
  Purchase #6 $249.31   4.700%   $261.0276   $261.03   $261.05   $261.00  
  Purchase #7 $190.81   5.549%   $201.398   $201.40   $201.40   $201.40  
  7 purchase totals = $1,223.24       $1,325.1116   $1,325.11   $1,325.10   $1,325.20