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 $39.62   4.596%   $41.4409   $41.44   $41.45   $41.40  
  Purchase #2 $136.90   8.277%   $148.2312   $148.23   $148.25   $148.20  
  Purchase #3 $233.79   7.658%   $251.6936   $251.69   $251.70   $251.70  
  Purchase #4 $63.37   4.798%   $66.4105   $66.41   $66.40   $66.40  
  Purchase #5 $116.42   5.186%   $122.4575   $122.46   $122.45   $122.50  
  Purchase #6 $228.70   8.261%   $247.5929   $247.59   $247.60   $247.60  
  Purchase #7 $74.90   9.145%   $81.7496   $81.75   $81.75   $81.70  
  7 purchase totals = $893.70       $959.5762   $959.57   $959.60   $959.50