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 $114.99   10.619%   $127.2008   $127.20   $127.20   $127.20  
  Purchase #2 $237.26   8.367%   $257.1115   $257.11   $257.10   $257.10  
  Purchase #3 $242.51   10.301%   $267.491   $267.49   $267.50   $267.50  
  Purchase #4 $21.59   13.142%   $24.4274   $24.43   $24.45   $24.40  
  Purchase #5 $108.73   3.500%   $112.5356   $112.54   $112.55   $112.50  
  Purchase #6 $49.87   3.361%   $51.5461   $51.55   $51.55   $51.50  
  Purchase #7 $110.41   7.752%   $118.969   $118.97   $118.95   $119.00  
  7 purchase totals = $885.36       $959.2814   $959.29   $959.30   $959.20