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 $249.75   5.233%   $262.8194   $262.82   $262.80   $262.80  
  Purchase #2 $123.67   11.869%   $138.3484   $138.35   $138.35   $138.30  
  Purchase #3 $20.41   3.538%   $21.1321   $21.13   $21.15   $21.10  
  Purchase #4 $37.85   10.356%   $41.7697   $41.77   $41.75   $41.80  
  Purchase #5 $96.70   10.292%   $106.6524   $106.65   $106.65   $106.70  
  Purchase #6 $183.81   12.577%   $206.9278   $206.93   $206.95   $206.90  
  Purchase #7 $73.77   6.203%   $78.346   $78.35   $78.35   $78.30  
  7 purchase totals = $785.96       $855.9958   $856.00   $856.00   $855.90