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 $219.81   13.437%   $249.3459   $249.35   $249.35   $249.30  
  Purchase #2 $28.97   11.498%   $32.301   $32.30   $32.30   $32.30  
  Purchase #3 $164.83   4.248%   $171.832   $171.83   $171.85   $171.80  
  Purchase #4 $65.30   3.660%   $67.69   $67.69   $67.70   $67.70  
  Purchase #5 $9.61   8.215%   $10.3995   $10.40   $10.40   $10.40  
  Purchase #6 $247.96   7.673%   $266.986   $266.99   $267.00   $267.00  
  Purchase #7 $223.47   11.830%   $249.9065   $249.91   $249.90   $249.90  
  7 purchase totals = $959.95       $1,048.4609   $1,048.47   $1,048.50   $1,048.40