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 $213.77   12.752%   $241.03   $241.03   $241.05   $241.00  
  Purchase #2 $208.34   7.863%   $224.7218   $224.72   $224.70   $224.70  
  Purchase #3 $227.29   8.125%   $245.7573   $245.76   $245.75   $245.80  
  Purchase #4 $27.40   8.624%   $29.763   $29.76   $29.75   $29.80  
  Purchase #5 $111.55   3.819%   $115.8101   $115.81   $115.80   $115.80  
  Purchase #6 $130.37   11.634%   $145.5372   $145.54   $145.55   $145.50  
  Purchase #7 $69.91   4.490%   $73.049   $73.05   $73.05   $73.00  
  7 purchase totals = $988.63       $1,075.6684   $1,075.67   $1,075.65   $1,075.60