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 $45.66   13.120%   $51.6506   $51.65   $51.65   $51.70  
  Purchase #2 $131.93   8.660%   $143.3551   $143.36   $143.35   $143.40  
  Purchase #3 $34.60   7.707%   $37.2666   $37.27   $37.25   $37.30  
  Purchase #4 $207.55   9.650%   $227.5786   $227.58   $227.60   $227.60  
  Purchase #5 $180.63   13.865%   $205.6743   $205.67   $205.65   $205.70  
  Purchase #6 $19.41   11.817%   $21.7037   $21.70   $21.70   $21.70  
  Purchase #7 $34.69   8.630%   $37.6837   $37.68   $37.70   $37.70  
  7 purchase totals = $654.47       $724.9126   $724.91   $724.90   $725.10