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 $124.70   13.602%   $141.6617   $141.66   $141.65   $141.70  
  Purchase #2 $113.37   11.490%   $126.3962   $126.40   $126.40   $126.40  
  Purchase #3 $81.33   11.456%   $90.6472   $90.65   $90.65   $90.60  
  Purchase #4 $224.88   7.808%   $242.4386   $242.44   $242.45   $242.40  
  Purchase #5 $120.30   8.668%   $130.7276   $130.73   $130.75   $130.70  
  Purchase #6 $239.67   8.228%   $259.39   $259.39   $259.40   $259.40  
  Purchase #7 $72.95   6.756%   $77.8785   $77.88   $77.90   $77.90  
  7 purchase totals = $977.20       $1,069.1398   $1,069.15   $1,069.20   $1,069.10