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 $126.55   6.143%   $134.324   $134.32   $134.30   $134.30  
  Purchase #2 $228.28   6.426%   $242.9493   $242.95   $242.95   $242.90  
  Purchase #3 $250.99   3.738%   $260.372   $260.37   $260.35   $260.40  
  Purchase #4 $237.30   4.770%   $248.6192   $248.62   $248.60   $248.60  
  Purchase #5 $132.59   6.777%   $141.5756   $141.58   $141.60   $141.60  
  Purchase #6 $75.45   9.624%   $82.7113   $82.71   $82.70   $82.70  
  Purchase #7 $125.49   8.414%   $136.0487   $136.05   $136.05   $136.00  
  7 purchase totals = $1,176.65       $1,246.6001   $1,246.60   $1,246.55   $1,246.50