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 $131.26   10.500%   $145.0423   $145.04   $145.05   $145.00  
  Purchase #2 $20.72   4.538%   $21.6603   $21.66   $21.65   $21.70  
  Purchase #3 $139.55   12.618%   $157.1584   $157.16   $157.15   $157.20  
  Purchase #4 $20.64   3.254%   $21.3116   $21.31   $21.30   $21.30  
  Purchase #5 $27.93   9.335%   $30.5373   $30.54   $30.55   $30.50  
  Purchase #6 $163.90   8.723%   $178.197   $178.20   $178.20   $178.20  
  Purchase #7 $149.88   8.608%   $162.7817   $162.78   $162.80   $162.80  
  7 purchase totals = $653.88       $716.6886   $716.69   $716.70   $716.70