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 $114.52   10.768%   $126.8515   $126.85   $126.85   $126.90  
  Purchase #2 $105.42   8.826%   $114.7244   $114.72   $114.70   $114.70  
  Purchase #3 $155.26   13.373%   $176.0229   $176.02   $176.00   $176.00  
  Purchase #4 $215.37   9.675%   $236.207   $236.21   $236.20   $236.20  
  Purchase #5 $199.97   4.467%   $208.9027   $208.90   $208.90   $208.90  
  Purchase #6 $179.26   9.619%   $196.503   $196.50   $196.50   $196.50  
  Purchase #7 $222.79   12.540%   $250.7279   $250.73   $250.75   $250.70  
  7 purchase totals = $1,192.59       $1,309.9394   $1,309.93   $1,309.90   $1,309.90