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 $151.30   11.457%   $168.6344   $168.63   $168.65   $168.60  
  Purchase #2 $214.85   8.405%   $232.9081   $232.91   $232.90   $232.90  
  Purchase #3 $171.58   7.796%   $184.9564   $184.96   $184.95   $185.00  
  Purchase #4 $176.58   12.557%   $198.7532   $198.75   $198.75   $198.80  
  Purchase #5 $77.97   5.451%   $82.2201   $82.22   $82.20   $82.20  
  Purchase #6 $198.44   8.863%   $216.0277   $216.03   $216.05   $216.00  
  Purchase #7 $180.43   10.650%   $199.6458   $199.65   $199.65   $199.60  
  7 purchase totals = $1,171.15       $1,283.1457   $1,283.15   $1,283.15   $1,283.10