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 $217.92   13.629%   $247.6203   $247.62   $247.60   $247.60  
  Purchase #2 $107.45   6.522%   $114.4579   $114.46   $114.45   $114.50  
  Purchase #3 $57.98   6.738%   $61.8867   $61.89   $61.90   $61.90  
  Purchase #4 $166.41   4.746%   $174.3078   $174.31   $174.30   $174.30  
  Purchase #5 $242.76   13.252%   $274.9306   $274.93   $274.95   $274.90  
  Purchase #6 $147.86   11.555%   $164.9452   $164.95   $164.95   $164.90  
  Purchase #7 $156.77   4.474%   $163.7839   $163.78   $163.80   $163.80  
  7 purchase totals = $1,097.15       $1,201.9324   $1,201.94   $1,201.95   $1,201.90