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 $89.33   7.379%   $95.9217   $95.92   $95.90   $95.90  
  Purchase #2 $72.42   6.224%   $76.9274   $76.93   $76.95   $76.90  
  Purchase #3 $228.93   3.828%   $237.6934   $237.69   $237.70   $237.70  
  Purchase #4 $108.94   9.556%   $119.3503   $119.35   $119.35   $119.40  
  Purchase #5 $221.82   7.552%   $238.5718   $238.57   $238.55   $238.60  
  Purchase #6 $17.36   5.792%   $18.3655   $18.37   $18.35   $18.40  
  Purchase #7 $173.72   13.455%   $197.094   $197.09   $197.10   $197.10  
  7 purchase totals = $912.52       $983.9241   $983.92   $983.90   $984.00