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 $214.53   6.501%   $228.4766   $228.48   $228.50   $228.50  
  Purchase #2 $144.91   9.266%   $158.3374   $158.34   $158.35   $158.30  
  Purchase #3 $28.39   12.724%   $32.0023   $32.00   $32.00   $32.00  
  Purchase #4 $39.97   6.296%   $42.4865   $42.49   $42.50   $42.50  
  Purchase #5 $236.40   12.538%   $266.0398   $266.04   $266.05   $266.00  
  Purchase #6 $69.89   9.567%   $76.5764   $76.58   $76.60   $76.60  
  Purchase #7 $246.70   5.705%   $260.7742   $260.77   $260.75   $260.80  
  7 purchase totals = $980.79       $1,064.6932   $1,064.70   $1,064.75   $1,064.70