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 $61.38   13.422%   $69.6184   $69.62   $69.60   $69.60  
  Purchase #2 $224.87   12.617%   $253.2418   $253.24   $253.25   $253.20  
  Purchase #3 $11.41   13.557%   $12.9569   $12.96   $12.95   $13.00  
  Purchase #4 $114.81   8.597%   $124.6802   $124.68   $124.70   $124.70  
  Purchase #5 $249.48   12.409%   $280.438   $280.44   $280.45   $280.40  
  Purchase #6 $249.54   10.759%   $276.388   $276.39   $276.40   $276.40  
  Purchase #7 $8.37   8.211%   $9.0573   $9.06   $9.05   $9.10  
  7 purchase totals = $919.86       $1,026.3806   $1,026.39   $1,026.40   $1,026.40