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 $110.63   3.115%   $114.0761   $114.08   $114.10   $114.10  
  Purchase #2 $242.63   4.252%   $252.9466   $252.95   $252.95   $252.90  
  Purchase #3 $69.76   8.195%   $75.4768   $75.48   $75.50   $75.50  
  Purchase #4 $91.65   9.392%   $100.2578   $100.26   $100.25   $100.30  
  Purchase #5 $21.81   13.322%   $24.7155   $24.72   $24.70   $24.70  
  Purchase #6 $88.41   4.159%   $92.087   $92.09   $92.10   $92.10  
  Purchase #7 $135.27   4.311%   $141.1015   $141.10   $141.10   $141.10  
  7 purchase totals = $760.16       $800.6613   $800.68   $800.70   $800.70