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 $213.66   13.563%   $242.6387   $242.64   $242.65   $242.60  
  Purchase #2 $40.33   7.626%   $43.4056   $43.41   $43.40   $43.40  
  Purchase #3 $179.36   5.764%   $189.6983   $189.70   $189.70   $189.70  
  Purchase #4 $244.38   7.349%   $262.3395   $262.34   $262.35   $262.30  
  Purchase #5 $152.55   7.686%   $164.275   $164.28   $164.30   $164.30  
  Purchase #6 $141.27   10.648%   $156.3124   $156.31   $156.30   $156.30  
  Purchase #7 $17.44   8.545%   $18.9302   $18.93   $18.95   $18.90  
  7 purchase totals = $988.99       $1,077.5997   $1,077.61   $1,077.65   $1,077.50