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 $62.39   10.421%   $68.8917   $68.89   $68.90   $68.90  
  Purchase #2 $214.76   6.554%   $228.8354   $228.84   $228.85   $228.80  
  Purchase #3 $125.96   6.202%   $133.772   $133.77   $133.75   $133.80  
  Purchase #4 $195.44   5.681%   $206.5429   $206.54   $206.55   $206.50  
  Purchase #5 $66.94   11.249%   $74.4701   $74.47   $74.45   $74.50  
  Purchase #6 $23.71   11.262%   $26.3802   $26.38   $26.40   $26.40  
  Purchase #7 $121.32   4.228%   $126.4494   $126.45   $126.45   $126.40  
  7 purchase totals = $810.52       $865.3417   $865.34   $865.35   $865.30