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 $22.28   11.361%   $24.8112   $24.81   $24.80   $24.80  
  Purchase #2 $217.58   10.649%   $240.7501   $240.75   $240.75   $240.80  
  Purchase #3 $145.57   7.473%   $156.4484   $156.45   $156.45   $156.40  
  Purchase #4 $227.98   13.780%   $259.3956   $259.40   $259.40   $259.40  
  Purchase #5 $140.68   5.456%   $148.3555   $148.36   $148.35   $148.40  
  Purchase #6 $104.69   9.545%   $114.6827   $114.68   $114.70   $114.70  
  Purchase #7 $92.67   6.224%   $98.4378   $98.44   $98.45   $98.40  
  7 purchase totals = $951.45       $1,042.8813   $1,042.89   $1,042.90   $1,042.90