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 $57.60   9.119%   $62.8525   $62.85   $62.85   $62.90  
  Purchase #2 $184.41   10.169%   $203.1627   $203.16   $203.15   $203.20  
  Purchase #3 $24.95   13.203%   $28.2441   $28.24   $28.25   $28.20  
  Purchase #4 $6.78   11.722%   $7.5748   $7.57   $7.55   $7.60  
  Purchase #5 $186.62   11.246%   $207.6073   $207.61   $207.60   $207.60  
  Purchase #6 $182.40   6.106%   $193.5373   $193.54   $193.55   $193.50  
  Purchase #7 $178.37   13.507%   $202.4624   $202.46   $202.45   $202.50  
  7 purchase totals = $821.13       $905.4411   $905.43   $905.40   $905.50