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 $243.86   6.402%   $259.4719   $259.47   $259.45   $259.50  
  Purchase #2 $39.41   8.149%   $42.6215   $42.62   $42.60   $42.60  
  Purchase #3 $241.35   5.667%   $255.0273   $255.03   $255.05   $255.00  
  Purchase #4 $218.55   5.542%   $230.662   $230.66   $230.65   $230.70  
  Purchase #5 $171.58   8.166%   $185.5912   $185.59   $185.60   $185.60  
  Purchase #6 $91.28   8.253%   $98.8133   $98.81   $98.80   $98.80  
  Purchase #7 $129.65   5.378%   $136.6226   $136.62   $136.60   $136.60  
  7 purchase totals = $1,135.68       $1,208.8098   $1,208.80   $1,208.75   $1,208.80