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 $38.84   6.866%   $41.5068   $41.51   $41.50   $41.50  
  Purchase #2 $123.67   13.451%   $140.3049   $140.30   $140.30   $140.30  
  Purchase #3 $188.40   5.831%   $199.3856   $199.39   $199.40   $199.40  
  Purchase #4 $182.85   6.831%   $195.3405   $195.34   $195.35   $195.30  
  Purchase #5 $172.45   11.763%   $192.7353   $192.74   $192.75   $192.70  
  Purchase #6 $207.63   3.376%   $214.6396   $214.64   $214.65   $214.60  
  Purchase #7 $63.97   13.528%   $72.6239   $72.62   $72.60   $72.60  
  7 purchase totals = $977.81       $1,056.5366   $1,056.54   $1,056.55   $1,056.40