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 $63.44   3.103%   $65.4085   $65.41   $65.40   $65.40  
  Purchase #2 $244.41   9.176%   $266.8371   $266.84   $266.85   $266.80  
  Purchase #3 $38.38   13.120%   $43.4155   $43.42   $43.40   $43.40  
  Purchase #4 $38.50   9.305%   $42.0824   $42.08   $42.10   $42.10  
  Purchase #5 $228.72   5.653%   $241.6495   $241.65   $241.65   $241.60  
  Purchase #6 $194.44   12.161%   $218.0858   $218.09   $218.10   $218.10  
  Purchase #7 $74.39   4.736%   $77.9131   $77.91   $77.90   $77.90  
  7 purchase totals = $882.28       $955.3919   $955.40   $955.40   $955.30