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 $111.53   7.452%   $119.8412   $119.84   $119.85   $119.80  
  Purchase #2 $122.41   3.824%   $127.091   $127.09   $127.10   $127.10  
  Purchase #3 $176.83   9.616%   $193.834   $193.83   $193.85   $193.80  
  Purchase #4 $46.58   10.627%   $51.5301   $51.53   $51.55   $51.50  
  Purchase #5 $159.54   10.712%   $176.6299   $176.63   $176.65   $176.60  
  Purchase #6 $109.75   3.144%   $113.2005   $113.20   $113.20   $113.20  
  Purchase #7 $112.63   12.308%   $126.4925   $126.49   $126.50   $126.50  
  7 purchase totals = $839.27       $908.6192   $908.61   $908.70   $908.50