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 $87.92   11.617%   $98.1337   $98.13   $98.15   $98.10  
  Purchase #2 $149.78   5.171%   $157.5251   $157.53   $157.55   $157.50  
  Purchase #3 $163.32   8.736%   $177.5876   $177.59   $177.60   $177.60  
  Purchase #4 $195.85   6.647%   $208.8681   $208.87   $208.85   $208.90  
  Purchase #5 $42.56   13.859%   $48.4584   $48.46   $48.45   $48.50  
  Purchase #6 $127.84   5.791%   $135.2432   $135.24   $135.25   $135.20  
  Purchase #7 $120.61   4.548%   $126.0953   $126.10   $126.10   $126.10  
  7 purchase totals = $887.88       $951.9114   $951.92   $951.95   $951.90