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 $230.58   13.752%   $262.2894   $262.29   $262.30   $262.30  
  Purchase #2 $217.82   4.267%   $227.1144   $227.11   $227.10   $227.10  
  Purchase #3 $38.25   12.829%   $43.1571   $43.16   $43.15   $43.20  
  Purchase #4 $24.64   7.120%   $26.3944   $26.39   $26.40   $26.40  
  Purchase #5 $58.78   9.324%   $64.2606   $64.26   $64.25   $64.30  
  Purchase #6 $143.97   13.586%   $163.5298   $163.53   $163.55   $163.50  
  Purchase #7 $178.68   4.393%   $186.5294   $186.53   $186.55   $186.50  
  7 purchase totals = $892.72       $973.2751   $973.27   $973.30   $973.30