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 $53.38   13.562%   $60.6194   $60.62   $60.60   $60.60  
  Purchase #2 $124.75   10.491%   $137.8375   $137.84   $137.85   $137.80  
  Purchase #3 $19.99   5.427%   $21.0749   $21.07   $21.05   $21.10  
  Purchase #4 $139.92   12.515%   $157.431   $157.43   $157.45   $157.40  
  Purchase #5 $239.83   12.309%   $269.3507   $269.35   $269.35   $269.40  
  Purchase #6 $69.52   6.174%   $73.8122   $73.81   $73.80   $73.80  
  Purchase #7 $35.60   7.474%   $38.2607   $38.26   $38.25   $38.30  
  7 purchase totals = $682.99       $758.3864   $758.38   $758.35   $758.40