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 $231.95   13.368%   $262.9571   $262.96   $262.95   $263.00  
  Purchase #2 $115.97   8.575%   $125.9144   $125.91   $125.90   $125.90  
  Purchase #3 $196.55   13.187%   $222.469   $222.47   $222.45   $222.50  
  Purchase #4 $225.66   7.650%   $242.923   $242.92   $242.90   $242.90  
  Purchase #5 $204.75   8.831%   $222.8315   $222.83   $222.85   $222.80  
  Purchase #6 $70.87   8.177%   $76.665   $76.67   $76.65   $76.70  
  Purchase #7 $50.69   11.378%   $56.4575   $56.46   $56.45   $56.50  
  7 purchase totals = $1,096.44       $1,210.2175   $1,210.22   $1,210.15   $1,210.30