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 $242.66   8.231%   $262.6333   $262.63   $262.65   $262.60  
  Purchase #2 $166.85   10.830%   $184.9199   $184.92   $184.90   $184.90  
  Purchase #3 $175.72   4.577%   $183.7627   $183.76   $183.75   $183.80  
  Purchase #4 $83.34   3.704%   $86.4269   $86.43   $86.45   $86.40  
  Purchase #5 $58.66   11.508%   $65.4106   $65.41   $65.40   $65.40  
  Purchase #6 $159.95   4.377%   $166.951   $166.95   $166.95   $167.00  
  Purchase #7 $18.50   4.403%   $19.3146   $19.31   $19.30   $19.30  
  7 purchase totals = $905.68       $969.4190   $969.41   $969.40   $969.40