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 $20.41   11.848%   $22.8282   $22.83   $22.85   $22.80  
  Purchase #2 $92.55   13.371%   $104.9249   $104.92   $104.90   $104.90  
  Purchase #3 $153.55   13.677%   $174.551   $174.55   $174.55   $174.60  
  Purchase #4 $69.49   5.191%   $73.0972   $73.10   $73.10   $73.10  
  Purchase #5 $49.81   12.347%   $55.96   $55.96   $55.95   $56.00  
  Purchase #6 $218.98   7.791%   $236.0407   $236.04   $236.05   $236.00  
  Purchase #7 $235.78   5.592%   $248.9648   $248.96   $248.95   $249.00  
  7 purchase totals = $840.57       $916.3668   $916.36   $916.35   $916.40