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 $76.41   11.423%   $85.1383   $85.14   $85.15   $85.10  
  Purchase #2 $157.92   3.387%   $163.2688   $163.27   $163.25   $163.30  
  Purchase #3 $222.91   7.862%   $240.4352   $240.44   $240.45   $240.40  
  Purchase #4 $234.42   4.462%   $244.8798   $244.88   $244.90   $244.90  
  Purchase #5 $40.57   8.616%   $44.0655   $44.07   $44.05   $44.10  
  Purchase #6 $202.45   11.573%   $225.8795   $225.88   $225.90   $225.90  
  Purchase #7 $109.32   5.408%   $115.232   $115.23   $115.25   $115.20  
  7 purchase totals = $1,044.00       $1,118.8991   $1,118.91   $1,118.95   $1,118.90