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 $236.77   10.331%   $261.2307   $261.23   $261.25   $261.20  
  Purchase #2 $182.79   10.208%   $201.4492   $201.45   $201.45   $201.40  
  Purchase #3 $224.66   11.663%   $250.8621   $250.86   $250.85   $250.90  
  Purchase #4 $229.58   11.510%   $256.0047   $256.00   $256.00   $256.00  
  Purchase #5 $42.97   5.119%   $45.1696   $45.17   $45.15   $45.20  
  Purchase #6 $221.55   6.626%   $236.2299   $236.23   $236.25   $236.20  
  Purchase #7 $101.87   11.176%   $113.255   $113.26   $113.25   $113.30  
  7 purchase totals = $1,240.19       $1,364.2012   $1,364.20   $1,364.20   $1,364.20