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 $238.68   8.788%   $259.6552   $259.66   $259.65   $259.70  
  Purchase #2 $50.58   6.166%   $53.6988   $53.70   $53.70   $53.70  
  Purchase #3 $228.89   13.177%   $259.0508   $259.05   $259.05   $259.10  
  Purchase #4 $164.81   4.217%   $171.76   $171.76   $171.75   $171.80  
  Purchase #5 $174.92   9.181%   $190.9794   $190.98   $191.00   $191.00  
  Purchase #6 $207.76   9.357%   $227.2001   $227.20   $227.20   $227.20  
  Purchase #7 $12.46   13.398%   $14.1294   $14.13   $14.15   $14.10  
  7 purchase totals = $1,078.10       $1,176.4737   $1,176.48   $1,176.50   $1,176.60