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 $14.40   9.597%   $15.782   $15.78   $15.80   $15.80  
  Purchase #2 $35.50   8.403%   $38.4831   $38.48   $38.50   $38.50  
  Purchase #3 $184.26   13.212%   $208.6044   $208.60   $208.60   $208.60  
  Purchase #4 $134.82   3.547%   $139.6021   $139.60   $139.60   $139.60  
  Purchase #5 $162.32   4.750%   $170.0302   $170.03   $170.05   $170.00  
  Purchase #6 $119.81   6.841%   $128.0062   $128.01   $128.00   $128.00  
  Purchase #7 $174.73   13.433%   $198.2015   $198.20   $198.20   $198.20  
  7 purchase totals = $825.84       $898.7095   $898.70   $898.75   $898.70