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 $50.27   12.545%   $56.5764   $56.58   $56.60   $56.60  
  Purchase #2 $232.75   12.543%   $261.9438   $261.94   $261.95   $261.90  
  Purchase #3 $28.38   13.215%   $32.1304   $32.13   $32.15   $32.10  
  Purchase #4 $202.51   4.580%   $211.785   $211.79   $211.80   $211.80  
  Purchase #5 $12.55   4.119%   $13.0669   $13.07   $13.05   $13.10  
  Purchase #6 $58.61   12.327%   $65.8349   $65.83   $65.85   $65.80  
  Purchase #7 $250.60   5.839%   $265.2325   $265.23   $265.25   $265.20  
  7 purchase totals = $835.67       $906.5699   $906.57   $906.65   $906.50