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 $65.38   6.684%   $69.75   $69.75   $69.75   $69.80  
  Purchase #2 $45.76   4.366%   $47.7579   $47.76   $47.75   $47.80  
  Purchase #3 $92.81   5.863%   $98.2515   $98.25   $98.25   $98.30  
  Purchase #4 $29.59   10.822%   $32.7922   $32.79   $32.80   $32.80  
  Purchase #5 $106.26   9.838%   $116.7139   $116.71   $116.70   $116.70  
  Purchase #6 $205.29   9.342%   $224.4682   $224.47   $224.45   $224.50  
  Purchase #7 $157.88   4.466%   $164.9309   $164.93   $164.95   $164.90  
  7 purchase totals = $702.97       $754.6646   $754.66   $754.65   $754.80