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 $244.61   3.251%   $252.5623   $252.56   $252.55   $252.60  
  Purchase #2 $63.33   8.848%   $68.9334   $68.93   $68.95   $68.90  
  Purchase #3 $247.43   10.725%   $273.9669   $273.97   $273.95   $274.00  
  Purchase #4 $50.83   6.560%   $54.1644   $54.16   $54.15   $54.20  
  Purchase #5 $73.63   12.275%   $82.6681   $82.67   $82.65   $82.70  
  Purchase #6 $248.87   9.688%   $272.9805   $272.98   $273.00   $273.00  
  Purchase #7 $146.98   7.824%   $158.4797   $158.48   $158.50   $158.50  
  7 purchase totals = $1,075.68       $1,163.7553   $1,163.75   $1,163.75   $1,163.90