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 $216.68   3.659%   $224.6083   $224.61   $224.60   $224.60  
  Purchase #2 $164.58   5.355%   $173.3933   $173.39   $173.40   $173.40  
  Purchase #3 $44.72   6.231%   $47.5065   $47.51   $47.50   $47.50  
  Purchase #4 $116.66   4.652%   $122.087   $122.09   $122.10   $122.10  
  Purchase #5 $40.53   13.252%   $45.901   $45.90   $45.90   $45.90  
  Purchase #6 $116.99   7.407%   $125.6554   $125.66   $125.65   $125.70  
  Purchase #7 $228.39   12.409%   $256.7309   $256.73   $256.75   $256.70  
  7 purchase totals = $928.55       $995.8824   $995.89   $995.90   $995.90