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 $161.97   5.742%   $171.2703   $171.27   $171.25   $171.30  
  Purchase #2 $43.68   6.676%   $46.5961   $46.60   $46.60   $46.60  
  Purchase #3 $207.50   6.272%   $220.5144   $220.51   $220.50   $220.50  
  Purchase #4 $250.35   4.866%   $262.532   $262.53   $262.55   $262.50  
  Purchase #5 $111.83   12.301%   $125.5862   $125.59   $125.60   $125.60  
  Purchase #6 $180.99   13.632%   $205.6626   $205.66   $205.65   $205.70  
  Purchase #7 $143.89   5.556%   $151.8845   $151.88   $151.90   $151.90  
  7 purchase totals = $1,100.21       $1,184.0461   $1,184.04   $1,184.05   $1,184.10