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 $78.88   4.763%   $82.6371   $82.64   $82.65   $82.60  
  Purchase #2 $104.75   9.277%   $114.4677   $114.47   $114.45   $114.50  
  Purchase #3 $194.76   8.705%   $211.7139   $211.71   $211.70   $211.70  
  Purchase #4 $108.63   10.648%   $120.1969   $120.20   $120.20   $120.20  
  Purchase #5 $228.92   8.679%   $248.788   $248.79   $248.80   $248.80  
  Purchase #6 $180.37   8.487%   $195.678   $195.68   $195.70   $195.70  
  Purchase #7 $76.68   12.622%   $86.3585   $86.36   $86.35   $86.40  
  7 purchase totals = $972.99       $1,059.8401   $1,059.85   $1,059.85   $1,059.90