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 $56.83   11.863%   $63.5717   $63.57   $63.55   $63.60  
  Purchase #2 $213.89   11.817%   $239.1654   $239.17   $239.15   $239.20  
  Purchase #3 $104.77   12.666%   $118.0402   $118.04   $118.05   $118.00  
  Purchase #4 $199.75   11.377%   $222.4756   $222.48   $222.50   $222.50  
  Purchase #5 $240.48   5.675%   $254.1272   $254.13   $254.15   $254.10  
  Purchase #6 $153.81   13.515%   $174.5974   $174.60   $174.60   $174.60  
  Purchase #7 $248.47   4.242%   $259.0101   $259.01   $259.00   $259.00  
  7 purchase totals = $1,218.00       $1,330.9876   $1,331.00   $1,331.00   $1,331.00