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 $64.90   5.853%   $68.6986   $68.70   $68.70   $68.70  
  Purchase #2 $71.85   6.417%   $76.4606   $76.46   $76.45   $76.50  
  Purchase #3 $40.84   3.241%   $42.1636   $42.16   $42.15   $42.20  
  Purchase #4 $94.92   12.209%   $106.5088   $106.51   $106.50   $106.50  
  Purchase #5 $172.48   8.473%   $187.0942   $187.09   $187.10   $187.10  
  Purchase #6 $53.77   5.462%   $56.7069   $56.71   $56.70   $56.70  
  Purchase #7 $56.40   6.657%   $60.1545   $60.15   $60.15   $60.20  
  7 purchase totals = $555.16       $597.7872   $597.78   $597.75   $597.90