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 $87.26   12.518%   $98.1832   $98.18   $98.20   $98.20  
  Purchase #2 $53.76   4.447%   $56.1507   $56.15   $56.15   $56.20  
  Purchase #3 $130.25   9.299%   $142.3619   $142.36   $142.35   $142.40  
  Purchase #4 $151.97   10.387%   $167.7551   $167.76   $167.75   $167.80  
  Purchase #5 $151.83   10.406%   $167.6294   $167.63   $167.65   $167.60  
  Purchase #6 $249.76   4.712%   $261.5287   $261.53   $261.55   $261.50  
  Purchase #7 $204.81   10.396%   $226.102   $226.10   $226.10   $226.10  
  7 purchase totals = $1,029.64       $1,119.7110   $1,119.71   $1,119.75   $1,119.80