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 $249.76   4.541%   $261.1016   $261.10   $261.10   $261.10  
  Purchase #2 $41.66   6.234%   $44.2571   $44.26   $44.25   $44.30  
  Purchase #3 $143.69   4.781%   $150.5598   $150.56   $150.55   $150.60  
  Purchase #4 $218.63   4.711%   $228.9297   $228.93   $228.95   $228.90  
  Purchase #5 $124.86   7.400%   $134.0996   $134.10   $134.10   $134.10  
  Purchase #6 $156.39   3.284%   $161.5258   $161.53   $161.55   $161.50  
  Purchase #7 $22.25   11.617%   $24.8348   $24.83   $24.85   $24.80  
  7 purchase totals = $957.24       $1,005.3084   $1,005.31   $1,005.35   $1,005.30