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 $194.34   10.119%   $214.0053   $214.01   $214.00   $214.00  
  Purchase #2 $135.27   4.418%   $141.2462   $141.25   $141.25   $141.20  
  Purchase #3 $222.46   12.498%   $250.2631   $250.26   $250.25   $250.30  
  Purchase #4 $44.85   5.461%   $47.2993   $47.30   $47.30   $47.30  
  Purchase #5 $144.37   12.320%   $162.1564   $162.16   $162.15   $162.20  
  Purchase #6 $236.61   8.116%   $255.8133   $255.81   $255.80   $255.80  
  Purchase #7 $163.93   11.815%   $183.2983   $183.30   $183.30   $183.30  
  7 purchase totals = $1,141.83       $1,254.0819   $1,254.09   $1,254.05   $1,254.10