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 $168.65   10.329%   $186.0699   $186.07   $186.05   $186.10  
  Purchase #2 $124.74   9.150%   $136.1537   $136.15   $136.15   $136.20  
  Purchase #3 $219.87   6.366%   $233.8669   $233.87   $233.85   $233.90  
  Purchase #4 $203.63   5.357%   $214.5385   $214.54   $214.55   $214.50  
  Purchase #5 $43.95   13.477%   $49.8731   $49.87   $49.85   $49.90  
  Purchase #6 $233.91   11.359%   $260.4798   $260.48   $260.50   $260.50  
  Purchase #7 $26.25   12.830%   $29.6179   $29.62   $29.60   $29.60  
  7 purchase totals = $1,021.00       $1,110.5998   $1,110.60   $1,110.55   $1,110.70