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 $84.28   13.451%   $95.6165   $95.62   $95.60   $95.60  
  Purchase #2 $161.95   9.195%   $176.8413   $176.84   $176.85   $176.80  
  Purchase #3 $239.65   3.549%   $248.1552   $248.16   $248.15   $248.20  
  Purchase #4 $26.56   3.170%   $27.402   $27.40   $27.40   $27.40  
  Purchase #5 $52.81   6.456%   $56.2194   $56.22   $56.20   $56.20  
  Purchase #6 $112.47   8.171%   $121.6599   $121.66   $121.65   $121.70  
  Purchase #7 $228.93   8.513%   $248.4188   $248.42   $248.40   $248.40  
  7 purchase totals = $906.65       $974.3131   $974.32   $974.25   $974.30