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 $250.95   5.838%   $265.6005   $265.60   $265.60   $265.60  
  Purchase #2 $182.32   8.477%   $197.7753   $197.78   $197.80   $197.80  
  Purchase #3 $25.48   13.687%   $28.9674   $28.97   $28.95   $29.00  
  Purchase #4 $244.99   6.316%   $260.4636   $260.46   $260.45   $260.50  
  Purchase #5 $53.99   11.706%   $60.3101   $60.31   $60.30   $60.30  
  Purchase #6 $30.55   8.324%   $33.093   $33.09   $33.10   $33.10  
  Purchase #7 $241.43   7.496%   $259.5276   $259.53   $259.55   $259.50  
  7 purchase totals = $1,029.71       $1,105.7375   $1,105.74   $1,105.75   $1,105.80