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 $60.39   3.647%   $62.5924   $62.59   $62.60   $62.60  
  Purchase #2 $238.37   5.152%   $250.6508   $250.65   $250.65   $250.70  
  Purchase #3 $86.87   3.339%   $89.7706   $89.77   $89.75   $89.80  
  Purchase #4 $25.69   4.535%   $26.855   $26.86   $26.85   $26.90  
  Purchase #5 $237.60   13.732%   $270.2272   $270.23   $270.25   $270.20  
  Purchase #6 $207.90   8.200%   $224.9478   $224.95   $224.95   $224.90  
  Purchase #7 $49.91   5.173%   $52.4918   $52.49   $52.50   $52.50  
  7 purchase totals = $906.73       $977.5356   $977.54   $977.55   $977.60