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 $55.55   6.649%   $59.2435   $59.24   $59.25   $59.20  
  Purchase #2 $237.56   6.787%   $253.6832   $253.68   $253.70   $253.70  
  Purchase #3 $157.64   6.631%   $168.0931   $168.09   $168.10   $168.10  
  Purchase #4 $168.52   5.461%   $177.7229   $177.72   $177.70   $177.70  
  Purchase #5 $239.45   10.848%   $265.4255   $265.43   $265.45   $265.40  
  Purchase #6 $142.99   13.616%   $162.4595   $162.46   $162.45   $162.50  
  Purchase #7 $244.88   8.571%   $265.8687   $265.87   $265.85   $265.90  
  7 purchase totals = $1,246.59       $1,352.4964   $1,352.49   $1,352.50   $1,352.50