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 $207.89   13.597%   $236.1568   $236.16   $236.15   $236.20  
  Purchase #2 $215.86   6.593%   $230.0916   $230.09   $230.10   $230.10  
  Purchase #3 $56.58   5.705%   $59.8079   $59.81   $59.80   $59.80  
  Purchase #4 $76.94   5.743%   $81.3587   $81.36   $81.35   $81.40  
  Purchase #5 $55.92   7.364%   $60.0379   $60.04   $60.05   $60.00  
  Purchase #6 $22.45   7.114%   $24.0471   $24.05   $24.05   $24.00  
  Purchase #7 $67.60   13.295%   $76.5874   $76.59   $76.60   $76.60  
  7 purchase totals = $703.24       $768.0874   $768.10   $768.10   $768.10