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 $201.25   11.701%   $224.7983   $224.80   $224.80   $224.80  
  Purchase #2 $107.98   3.497%   $111.7561   $111.76   $111.75   $111.80  
  Purchase #3 $113.67   9.771%   $124.7767   $124.78   $124.80   $124.80  
  Purchase #4 $21.58   13.161%   $24.4201   $24.42   $24.40   $24.40  
  Purchase #5 $103.56   10.235%   $114.1594   $114.16   $114.15   $114.20  
  Purchase #6 $238.47   9.591%   $261.3417   $261.34   $261.35   $261.30  
  Purchase #7 $207.51   13.360%   $235.2333   $235.23   $235.25   $235.20  
  7 purchase totals = $994.02       $1,096.4856   $1,096.49   $1,096.50   $1,096.50