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 $181.97   12.565%   $204.8345   $204.83   $204.85   $204.80  
  Purchase #2 $248.99   4.711%   $260.7199   $260.72   $260.70   $260.70  
  Purchase #3 $24.63   12.670%   $27.7506   $27.75   $27.75   $27.80  
  Purchase #4 $48.38   9.546%   $52.9984   $53.00   $53.00   $53.00  
  Purchase #5 $16.53   5.238%   $17.3958   $17.40   $17.40   $17.40  
  Purchase #6 $15.76   11.422%   $17.5601   $17.56   $17.55   $17.60  
  Purchase #7 $143.33   7.573%   $154.1844   $154.18   $154.20   $154.20  
  7 purchase totals = $679.59       $735.4437   $735.44   $735.45   $735.50