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 $239.85   8.386%   $259.9638   $259.96   $259.95   $260.00  
  Purchase #2 $54.60   13.461%   $61.9497   $61.95   $61.95   $61.90  
  Purchase #3 $123.28   8.375%   $133.6047   $133.60   $133.60   $133.60  
  Purchase #4 $151.69   3.387%   $156.8277   $156.83   $156.85   $156.80  
  Purchase #5 $176.28   7.566%   $189.6173   $189.62   $189.60   $189.60  
  Purchase #6 $122.26   3.651%   $126.7237   $126.72   $126.70   $126.70  
  Purchase #7 $208.81   9.272%   $228.1709   $228.17   $228.15   $228.20  
  7 purchase totals = $1,076.77       $1,156.8578   $1,156.85   $1,156.80   $1,156.80