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 $210.63   11.394%   $234.6292   $234.63   $234.65   $234.60  
  Purchase #2 $228.61   12.626%   $257.4743   $257.47   $257.45   $257.50  
  Purchase #3 $36.34   13.775%   $41.3458   $41.35   $41.35   $41.30  
  Purchase #4 $182.67   8.661%   $198.491   $198.49   $198.50   $198.50  
  Purchase #5 $188.77   6.569%   $201.1703   $201.17   $201.15   $201.20  
  Purchase #6 $70.31   11.140%   $78.1425   $78.14   $78.15   $78.10  
  Purchase #7 $76.69   11.171%   $85.257   $85.26   $85.25   $85.30  
  7 purchase totals = $994.02       $1,096.5101   $1,096.51   $1,096.50   $1,096.50