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 $208.49   8.178%   $225.5403   $225.54   $225.55   $225.50  
  Purchase #2 $149.43   4.873%   $156.7117   $156.71   $156.70   $156.70  
  Purchase #3 $168.56   6.740%   $179.9209   $179.92   $179.90   $179.90  
  Purchase #4 $114.27   6.847%   $122.0941   $122.09   $122.10   $122.10  
  Purchase #5 $13.99   4.737%   $14.6527   $14.65   $14.65   $14.70  
  Purchase #6 $83.63   3.808%   $86.8146   $86.81   $86.80   $86.80  
  Purchase #7 $11.93   5.231%   $12.5541   $12.55   $12.55   $12.60  
  7 purchase totals = $750.30       $798.2884   $798.27   $798.25   $798.30