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 $49.76   10.709%   $55.0888   $55.09   $55.10   $55.10  
  Purchase #2 $235.56   11.604%   $262.8944   $262.89   $262.90   $262.90  
  Purchase #3 $108.62   6.344%   $115.5109   $115.51   $115.50   $115.50  
  Purchase #4 $198.63   11.110%   $220.6978   $220.70   $220.70   $220.70  
  Purchase #5 $246.93   4.669%   $258.4592   $258.46   $258.45   $258.50  
  Purchase #6 $121.34   11.181%   $134.907   $134.91   $134.90   $134.90  
  Purchase #7 $70.68   11.310%   $78.6739   $78.67   $78.65   $78.70  
  7 purchase totals = $1,031.52       $1,126.2320   $1,126.23   $1,126.20   $1,126.30