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 $163.94   7.773%   $176.6831   $176.68   $176.70   $176.70  
  Purchase #2 $113.70   7.864%   $122.6414   $122.64   $122.65   $122.60  
  Purchase #3 $24.95   13.783%   $28.3889   $28.39   $28.40   $28.40  
  Purchase #4 $233.39   12.174%   $261.8029   $261.80   $261.80   $261.80  
  Purchase #5 $249.72   9.474%   $273.3785   $273.38   $273.40   $273.40  
  Purchase #6 $207.54   9.205%   $226.6441   $226.64   $226.65   $226.60  
  Purchase #7 $28.79   5.546%   $30.3867   $30.39   $30.40   $30.40  
  7 purchase totals = $1,022.03       $1,119.9256   $1,119.92   $1,120.00   $1,119.90