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 $45.61   13.828%   $51.917   $51.92   $51.90   $51.90  
  Purchase #2 $14.41   5.405%   $15.1889   $15.19   $15.20   $15.20  
  Purchase #3 $122.62   6.246%   $130.2788   $130.28   $130.30   $130.30  
  Purchase #4 $53.42   12.144%   $59.9073   $59.91   $59.90   $59.90  
  Purchase #5 $239.61   5.353%   $252.4363   $252.44   $252.45   $252.40  
  Purchase #6 $154.75   5.252%   $162.8775   $162.88   $162.90   $162.90  
  Purchase #7 $39.65   6.856%   $42.3684   $42.37   $42.35   $42.40  
  7 purchase totals = $670.07       $714.9742   $714.99   $715.00   $715.00