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 $59.37   9.778%   $65.1752   $65.18   $65.20   $65.20  
  Purchase #2 $250.63   4.770%   $262.5851   $262.59   $262.60   $262.60  
  Purchase #3 $42.90   8.303%   $46.462   $46.46   $46.45   $46.50  
  Purchase #4 $183.58   12.162%   $205.907   $205.91   $205.90   $205.90  
  Purchase #5 $14.43   3.258%   $14.9001   $14.90   $14.90   $14.90  
  Purchase #6 $139.46   10.604%   $154.2483   $154.25   $154.25   $154.20  
  Purchase #7 $104.70   6.280%   $111.2752   $111.28   $111.30   $111.30  
  7 purchase totals = $795.07       $860.5529   $860.57   $860.60   $860.60