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 $46.92   13.476%   $53.2429   $53.24   $53.25   $53.20  
  Purchase #2 $124.62   10.495%   $137.6989   $137.70   $137.70   $137.70  
  Purchase #3 $232.36   12.564%   $261.5537   $261.55   $261.55   $261.60  
  Purchase #4 $163.33   7.442%   $175.485   $175.49   $175.50   $175.50  
  Purchase #5 $211.37   9.366%   $231.1669   $231.17   $231.15   $231.20  
  Purchase #6 $207.88   4.610%   $217.4633   $217.46   $217.45   $217.50  
  Purchase #7 $218.46   6.794%   $233.3022   $233.30   $233.30   $233.30  
  7 purchase totals = $1,204.94       $1,309.9129   $1,309.91   $1,309.90   $1,310.00