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 $23.63   10.166%   $26.0322   $26.03   $26.05   $26.00  
  Purchase #2 $65.89   5.447%   $69.479   $69.48   $69.50   $69.50  
  Purchase #3 $35.62   10.845%   $39.483   $39.48   $39.50   $39.50  
  Purchase #4 $233.99   5.348%   $246.5038   $246.50   $246.50   $246.50  
  Purchase #5 $196.49   3.133%   $202.646   $202.65   $202.65   $202.60  
  Purchase #6 $191.59   5.263%   $201.6734   $201.67   $201.65   $201.70  
  Purchase #7 $50.38   8.795%   $54.8109   $54.81   $54.80   $54.80  
  7 purchase totals = $797.59       $840.6283   $840.62   $840.65   $840.60