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 $89.78   3.571%   $92.986   $92.99   $93.00   $93.00  
  Purchase #2 $154.27   6.334%   $164.0415   $164.04   $164.05   $164.00  
  Purchase #3 $145.50   12.400%   $163.542   $163.54   $163.55   $163.50  
  Purchase #4 $208.68   12.256%   $234.2558   $234.26   $234.25   $234.30  
  Purchase #5 $220.59   13.645%   $250.6895   $250.69   $250.70   $250.70  
  Purchase #6 $139.26   9.151%   $152.0037   $152.00   $152.00   $152.00  
  Purchase #7 $8.61   10.434%   $9.5084   $9.51   $9.50   $9.50  
  7 purchase totals = $966.69       $1,067.0269   $1,067.03   $1,067.05   $1,067.00