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 $208.47   13.324%   $236.2465   $236.25   $236.25   $236.20  
  Purchase #2 $38.32   10.298%   $42.2662   $42.27   $42.25   $42.30  
  Purchase #3 $149.47   4.692%   $156.4831   $156.48   $156.50   $156.50  
  Purchase #4 $212.32   7.619%   $228.4967   $228.50   $228.50   $228.50  
  Purchase #5 $169.61   3.556%   $175.6413   $175.64   $175.65   $175.60  
  Purchase #6 $46.34   6.481%   $49.3433   $49.34   $49.35   $49.30  
  Purchase #7 $157.80   4.226%   $164.4686   $164.47   $164.45   $164.50  
  7 purchase totals = $982.33       $1,052.9457   $1,052.95   $1,052.95   $1,052.90