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 $86.51   12.823%   $97.6032   $97.60   $97.60   $97.60  
  Purchase #2 $187.43   5.603%   $197.9317   $197.93   $197.95   $197.90  
  Purchase #3 $191.96   10.819%   $212.7282   $212.73   $212.75   $212.70  
  Purchase #4 $97.76   3.458%   $101.1405   $101.14   $101.15   $101.10  
  Purchase #5 $203.58   6.367%   $216.5419   $216.54   $216.55   $216.50  
  Purchase #6 $67.28   6.579%   $71.7064   $71.71   $71.70   $71.70  
  Purchase #7 $100.93   13.169%   $114.2215   $114.22   $114.20   $114.20  
  7 purchase totals = $935.45       $1,011.8734   $1,011.87   $1,011.90   $1,011.70