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 $245.65   12.605%   $276.6142   $276.61   $276.60   $276.60  
  Purchase #2 $103.44   12.315%   $116.1786   $116.18   $116.20   $116.20  
  Purchase #3 $11.31   3.294%   $11.6826   $11.68   $11.70   $11.70  
  Purchase #4 $198.30   13.710%   $225.4869   $225.49   $225.50   $225.50  
  Purchase #5 $228.93   4.874%   $240.088   $240.09   $240.10   $240.10  
  Purchase #6 $182.81   9.704%   $200.5499   $200.55   $200.55   $200.50  
  Purchase #7 $237.98   11.400%   $265.1097   $265.11   $265.10   $265.10  
  7 purchase totals = $1,208.42       $1,335.7099   $1,335.71   $1,335.75   $1,335.70