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 $231.70   12.207%   $259.9836   $259.98   $260.00   $260.00  
  Purchase #2 $84.43   8.825%   $91.8809   $91.88   $91.90   $91.90  
  Purchase #3 $105.81   7.725%   $113.9838   $113.98   $114.00   $114.00  
  Purchase #4 $42.85   10.442%   $47.3244   $47.32   $47.30   $47.30  
  Purchase #5 $96.46   6.602%   $102.8283   $102.83   $102.85   $102.80  
  Purchase #6 $122.26   4.298%   $127.5147   $127.51   $127.50   $127.50  
  Purchase #7 $10.45   6.596%   $11.1393   $11.14   $11.15   $11.10  
  7 purchase totals = $693.96       $754.6550   $754.64   $754.70   $754.60