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 $24.91   6.620%   $26.559   $26.56   $26.55   $26.60  
  Purchase #2 $81.98   10.719%   $90.7674   $90.77   $90.75   $90.80  
  Purchase #3 $176.77   6.576%   $188.3944   $188.39   $188.40   $188.40  
  Purchase #4 $113.70   11.151%   $126.3787   $126.38   $126.40   $126.40  
  Purchase #5 $48.68   10.790%   $53.9326   $53.93   $53.95   $53.90  
  Purchase #6 $14.59   5.691%   $15.4203   $15.42   $15.40   $15.40  
  Purchase #7 $179.56   8.256%   $194.3845   $194.38   $194.40   $194.40  
  7 purchase totals = $640.19       $695.8369   $695.83   $695.85   $695.90