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 $208.81   12.842%   $235.6254   $235.63   $235.65   $235.60  
  Purchase #2 $193.54   7.447%   $207.9529   $207.95   $207.95   $208.00  
  Purchase #3 $35.59   4.282%   $37.114   $37.11   $37.10   $37.10  
  Purchase #4 $248.65   5.216%   $261.6196   $261.62   $261.60   $261.60  
  Purchase #5 $23.89   3.172%   $24.6478   $24.65   $24.65   $24.60  
  Purchase #6 $68.88   12.465%   $77.4659   $77.47   $77.45   $77.50  
  Purchase #7 $139.94   6.532%   $149.0809   $149.08   $149.10   $149.10  
  7 purchase totals = $919.30       $993.5065   $993.51   $993.50   $993.50