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 $205.30   13.538%   $233.0935   $233.09   $233.10   $233.10  
  Purchase #2 $222.93   13.190%   $252.3345   $252.33   $252.35   $252.30  
  Purchase #3 $106.75   8.239%   $115.5451   $115.55   $115.55   $115.50  
  Purchase #4 $232.77   5.586%   $245.7725   $245.77   $245.75   $245.80  
  Purchase #5 $77.72   10.793%   $86.1083   $86.11   $86.10   $86.10  
  Purchase #6 $140.93   11.594%   $157.2694   $157.27   $157.25   $157.30  
  Purchase #7 $226.76   9.477%   $248.25   $248.25   $248.25   $248.30  
  7 purchase totals = $1,213.16       $1,338.3733   $1,338.37   $1,338.35   $1,338.40