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 $60.89   7.502%   $65.458   $65.46   $65.45   $65.50  
  Purchase #2 $35.81   8.266%   $38.7701   $38.77   $38.75   $38.80  
  Purchase #3 $180.66   5.722%   $190.9974   $191.00   $191.00   $191.00  
  Purchase #4 $76.28   13.369%   $86.4779   $86.48   $86.50   $86.50  
  Purchase #5 $210.34   12.508%   $236.6493   $236.65   $236.65   $236.60  
  Purchase #6 $238.26   8.796%   $259.2173   $259.22   $259.20   $259.20  
  Purchase #7 $228.70   10.669%   $253.1   $253.10   $253.10   $253.10  
  7 purchase totals = $1,030.94       $1,130.6700   $1,130.68   $1,130.65   $1,130.70