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 $196.99   13.276%   $223.1424   $223.14   $223.15   $223.10  
  Purchase #2 $85.67   6.850%   $91.5384   $91.54   $91.55   $91.50  
  Purchase #3 $129.71   3.466%   $134.2057   $134.21   $134.20   $134.20  
  Purchase #4 $232.53   12.526%   $261.6567   $261.66   $261.65   $261.70  
  Purchase #5 $68.48   5.574%   $72.2971   $72.30   $72.30   $72.30  
  Purchase #6 $87.44   4.189%   $91.1029   $91.10   $91.10   $91.10  
  Purchase #7 $186.85   3.508%   $193.4047   $193.40   $193.40   $193.40  
  7 purchase totals = $987.67       $1,067.3479   $1,067.35   $1,067.35   $1,067.30