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 $218.68   13.520%   $248.2455   $248.25   $248.25   $248.20  
  Purchase #2 $114.67   11.565%   $127.9316   $127.93   $127.95   $127.90  
  Purchase #3 $97.75   4.580%   $102.227   $102.23   $102.25   $102.20  
  Purchase #4 $248.56   3.422%   $257.0657   $257.07   $257.05   $257.10  
  Purchase #5 $23.84   8.811%   $25.9405   $25.94   $25.95   $25.90  
  Purchase #6 $108.38   3.475%   $112.1462   $112.15   $112.15   $112.10  
  Purchase #7 $228.99   4.117%   $238.4175   $238.42   $238.40   $238.40  
  7 purchase totals = $1,040.87       $1,111.9740   $1,111.99   $1,112.00   $1,111.80