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 $49.42   13.439%   $56.0616   $56.06   $56.05   $56.10  
  Purchase #2 $239.93   12.674%   $270.3387   $270.34   $270.35   $270.30  
  Purchase #3 $61.32   13.373%   $69.5203   $69.52   $69.50   $69.50  
  Purchase #4 $30.71   6.589%   $32.7335   $32.73   $32.75   $32.70  
  Purchase #5 $76.78   5.342%   $80.8816   $80.88   $80.90   $80.90  
  Purchase #6 $125.47   6.868%   $134.0873   $134.09   $134.10   $134.10  
  Purchase #7 $175.66   6.417%   $186.9321   $186.93   $186.95   $186.90  
  7 purchase totals = $759.29       $830.5551   $830.55   $830.60   $830.50