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 $118.83   10.831%   $131.7005   $131.70   $131.70   $131.70  
  Purchase #2 $227.87   6.439%   $242.5425   $242.54   $242.55   $242.50  
  Purchase #3 $81.58   9.210%   $89.0935   $89.09   $89.10   $89.10  
  Purchase #4 $154.96   12.812%   $174.8135   $174.81   $174.80   $174.80  
  Purchase #5 $164.74   11.345%   $183.4298   $183.43   $183.45   $183.40  
  Purchase #6 $114.46   9.772%   $125.645   $125.65   $125.65   $125.60  
  Purchase #7 $36.63   11.628%   $40.8893   $40.89   $40.90   $40.90  
  7 purchase totals = $899.07       $988.1141   $988.11   $988.15   $988.00