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 $205.67   12.273%   $230.9119   $230.91   $230.90   $230.90  
  Purchase #2 $188.60   9.683%   $206.8621   $206.86   $206.85   $206.90  
  Purchase #3 $10.38   7.531%   $11.1617   $11.16   $11.15   $11.20  
  Purchase #4 $91.50   6.159%   $97.1355   $97.14   $97.15   $97.10  
  Purchase #5 $67.43   3.165%   $69.5642   $69.56   $69.55   $69.60  
  Purchase #6 $121.57   13.145%   $137.5504   $137.55   $137.55   $137.60  
  Purchase #7 $233.93   11.600%   $261.0659   $261.07   $261.05   $261.10  
  7 purchase totals = $919.08       $1,014.2517   $1,014.25   $1,014.20   $1,014.40