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 $59.63   9.846%   $65.5012   $65.50   $65.50   $65.50  
  Purchase #2 $135.62   3.713%   $140.6556   $140.66   $140.65   $140.70  
  Purchase #3 $248.45   12.488%   $279.4764   $279.48   $279.50   $279.50  
  Purchase #4 $208.83   12.491%   $234.915   $234.92   $234.90   $234.90  
  Purchase #5 $157.37   4.610%   $164.6248   $164.62   $164.60   $164.60  
  Purchase #6 $221.85   6.107%   $235.3984   $235.40   $235.40   $235.40  
  Purchase #7 $114.41   7.217%   $122.667   $122.67   $122.65   $122.70  
  7 purchase totals = $1,146.16       $1,243.2384   $1,243.25   $1,243.20   $1,243.30