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 $201.64   3.504%   $208.7055   $208.71   $208.70   $208.70  
  Purchase #2 $144.82   12.311%   $162.6488   $162.65   $162.65   $162.60  
  Purchase #3 $224.49   8.778%   $244.1957   $244.20   $244.20   $244.20  
  Purchase #4 $134.75   9.524%   $147.5836   $147.58   $147.60   $147.60  
  Purchase #5 $64.32   6.271%   $68.3535   $68.35   $68.35   $68.40  
  Purchase #6 $247.36   7.676%   $266.3474   $266.35   $266.35   $266.30  
  Purchase #7 $242.39   7.465%   $260.4844   $260.48   $260.50   $260.50  
  7 purchase totals = $1,259.77       $1,358.3189   $1,358.32   $1,358.35   $1,358.30