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 $233.88   9.293%   $255.6145   $255.61   $255.60   $255.60  
  Purchase #2 $109.74   7.211%   $117.6534   $117.65   $117.65   $117.70  
  Purchase #3 $241.32   12.794%   $272.1945   $272.19   $272.20   $272.20  
  Purchase #4 $227.30   8.613%   $246.8773   $246.88   $246.90   $246.90  
  Purchase #5 $140.79   8.710%   $153.0528   $153.05   $153.05   $153.10  
  Purchase #6 $122.45   6.384%   $130.2672   $130.27   $130.25   $130.30  
  Purchase #7 $27.80   9.821%   $30.5302   $30.53   $30.55   $30.50  
  7 purchase totals = $1,103.28       $1,206.1899   $1,206.18   $1,206.20   $1,206.30