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 $241.31   8.473%   $261.7562   $261.76   $261.75   $261.80  
  Purchase #2 $167.46   6.455%   $178.2695   $178.27   $178.25   $178.30  
  Purchase #3 $129.48   7.492%   $139.1806   $139.18   $139.20   $139.20  
  Purchase #4 $155.44   3.565%   $160.9814   $160.98   $161.00   $161.00  
  Purchase #5 $151.81   5.534%   $160.2112   $160.21   $160.20   $160.20  
  Purchase #6 $40.73   9.579%   $44.6315   $44.63   $44.65   $44.60  
  Purchase #7 $106.88   4.335%   $111.5132   $111.51   $111.50   $111.50  
  7 purchase totals = $993.11       $1,056.5436   $1,056.54   $1,056.55   $1,056.60