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 $236.68   6.854%   $252.902   $252.90   $252.90   $252.90  
  Purchase #2 $50.55   12.626%   $56.9324   $56.93   $56.95   $56.90  
  Purchase #3 $23.60   5.517%   $24.902   $24.90   $24.90   $24.90  
  Purchase #4 $227.35   10.430%   $251.0626   $251.06   $251.05   $251.10  
  Purchase #5 $53.81   8.256%   $58.2526   $58.25   $58.25   $58.30  
  Purchase #6 $48.95   13.818%   $55.7139   $55.71   $55.70   $55.70  
  Purchase #7 $171.32   9.684%   $187.9106   $187.91   $187.90   $187.90  
  7 purchase totals = $812.26       $887.6761   $887.66   $887.65   $887.70