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 $63.31   8.682%   $68.8066   $68.81   $68.80   $68.80  
  Purchase #2 $199.38   7.673%   $214.6784   $214.68   $214.70   $214.70  
  Purchase #3 $81.44   3.464%   $84.2611   $84.26   $84.25   $84.30  
  Purchase #4 $179.52   8.574%   $194.912   $194.91   $194.90   $194.90  
  Purchase #5 $154.30   12.617%   $173.768   $173.77   $173.75   $173.80  
  Purchase #6 $124.45   13.342%   $141.0541   $141.05   $141.05   $141.10  
  Purchase #7 $54.29   7.336%   $58.2727   $58.27   $58.25   $58.30  
  7 purchase totals = $856.69       $935.7529   $935.75   $935.70   $935.90