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 $235.36   13.341%   $266.7594   $266.76   $266.75   $266.80  
  Purchase #2 $182.84   10.608%   $202.2357   $202.24   $202.25   $202.20  
  Purchase #3 $45.48   11.423%   $50.6752   $50.68   $50.70   $50.70  
  Purchase #4 $49.83   11.635%   $55.6277   $55.63   $55.65   $55.60  
  Purchase #5 $141.69   8.113%   $153.1853   $153.19   $153.20   $153.20  
  Purchase #6 $242.28   10.239%   $267.087   $267.09   $267.10   $267.10  
  Purchase #7 $222.27   12.759%   $250.6294   $250.63   $250.65   $250.60  
  7 purchase totals = $1,119.75       $1,246.1997   $1,246.22   $1,246.30   $1,246.20