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 $57.27   13.571%   $65.0421   $65.04   $65.05   $65.00  
  Purchase #2 $181.73   5.458%   $191.6488   $191.65   $191.65   $191.60  
  Purchase #3 $233.38   6.484%   $248.5124   $248.51   $248.50   $248.50  
  Purchase #4 $109.40   12.477%   $123.0498   $123.05   $123.05   $123.00  
  Purchase #5 $221.46   8.771%   $240.8843   $240.88   $240.90   $240.90  
  Purchase #6 $71.31   7.220%   $76.4586   $76.46   $76.45   $76.50  
  Purchase #7 $241.69   4.497%   $252.5588   $252.56   $252.55   $252.60  
  7 purchase totals = $1,116.24       $1,198.1548   $1,198.15   $1,198.15   $1,198.10