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 $191.78   8.457%   $207.9988   $208.00   $208.00   $208.00  
  Purchase #2 $111.88   9.627%   $122.6507   $122.65   $122.65   $122.70  
  Purchase #3 $214.76   11.745%   $239.9836   $239.98   $240.00   $240.00  
  Purchase #4 $41.29   9.196%   $45.087   $45.09   $45.10   $45.10  
  Purchase #5 $35.95   3.757%   $37.3006   $37.30   $37.30   $37.30  
  Purchase #6 $6.66   7.621%   $7.1676   $7.17   $7.15   $7.20  
  Purchase #7 $155.40   8.104%   $167.9936   $167.99   $168.00   $168.00  
  7 purchase totals = $757.72       $828.1819   $828.18   $828.20   $828.30