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 $213.65   10.796%   $236.7157   $236.72   $236.70   $236.70  
  Purchase #2 $163.47   12.328%   $183.6226   $183.62   $183.60   $183.60  
  Purchase #3 $121.42   3.295%   $125.4208   $125.42   $125.40   $125.40  
  Purchase #4 $67.45   13.449%   $76.5214   $76.52   $76.50   $76.50  
  Purchase #5 $136.67   8.580%   $148.3963   $148.40   $148.40   $148.40  
  Purchase #6 $133.38   5.318%   $140.4731   $140.47   $140.45   $140.50  
  Purchase #7 $101.48   3.574%   $105.1069   $105.11   $105.10   $105.10  
  7 purchase totals = $937.52       $1,016.2568   $1,016.26   $1,016.15   $1,016.20