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 $242.94   10.427%   $268.2714   $268.27   $268.25   $268.30  
  Purchase #2 $58.80   5.162%   $61.8353   $61.84   $61.85   $61.80  
  Purchase #3 $226.57   13.128%   $256.3141   $256.31   $256.30   $256.30  
  Purchase #4 $92.25   5.793%   $97.594   $97.59   $97.60   $97.60  
  Purchase #5 $171.29   7.273%   $183.7479   $183.75   $183.75   $183.70  
  Purchase #6 $240.40   3.473%   $248.7491   $248.75   $248.75   $248.70  
  Purchase #7 $205.57   8.349%   $222.733   $222.73   $222.75   $222.70  
  7 purchase totals = $1,237.82       $1,339.2448   $1,339.24   $1,339.25   $1,339.10