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 $228.98   5.460%   $241.4823   $241.48   $241.50   $241.50  
  Purchase #2 $97.50   9.791%   $107.0462   $107.05   $107.05   $107.00  
  Purchase #3 $181.42   3.868%   $188.4373   $188.44   $188.45   $188.40  
  Purchase #4 $183.88   4.544%   $192.2355   $192.24   $192.25   $192.20  
  Purchase #5 $179.32   6.469%   $190.9202   $190.92   $190.90   $190.90  
  Purchase #6 $80.56   7.527%   $86.6238   $86.62   $86.60   $86.60  
  Purchase #7 $229.38   13.110%   $259.4517   $259.45   $259.45   $259.50  
  7 purchase totals = $1,181.04       $1,266.1970   $1,266.20   $1,266.20   $1,266.10