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 $24.88   6.418%   $26.4768   $26.48   $26.50   $26.50  
  Purchase #2 $57.70   13.732%   $65.6234   $65.62   $65.60   $65.60  
  Purchase #3 $168.65   4.177%   $175.6945   $175.69   $175.70   $175.70  
  Purchase #4 $224.29   5.188%   $235.9262   $235.93   $235.95   $235.90  
  Purchase #5 $242.54   11.351%   $270.0707   $270.07   $270.05   $270.10  
  Purchase #6 $81.73   4.488%   $85.398   $85.40   $85.40   $85.40  
  Purchase #7 $5.26   9.408%   $5.7549   $5.75   $5.75   $5.80  
  7 purchase totals = $805.05       $864.9445   $864.94   $864.95   $865.00