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 $230.90   4.605%   $241.5329   $241.53   $241.55   $241.50  
  Purchase #2 $244.41   4.615%   $255.6895   $255.69   $255.70   $255.70  
  Purchase #3 $76.72   7.382%   $82.3835   $82.38   $82.40   $82.40  
  Purchase #4 $65.25   5.328%   $68.7265   $68.73   $68.75   $68.70  
  Purchase #5 $130.43   13.697%   $148.295   $148.30   $148.30   $148.30  
  Purchase #6 $26.79   8.326%   $29.0205   $29.02   $29.00   $29.00  
  Purchase #7 $121.55   11.327%   $135.318   $135.32   $135.30   $135.30  
  7 purchase totals = $896.05       $960.9659   $960.97   $961.00   $960.90