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 $49.94   7.354%   $53.6126   $53.61   $53.60   $53.60  
  Purchase #2 $68.71   8.537%   $74.5758   $74.58   $74.60   $74.60  
  Purchase #3 $147.82   4.670%   $154.7232   $154.72   $154.70   $154.70  
  Purchase #4 $178.53   4.699%   $186.9191   $186.92   $186.90   $186.90  
  Purchase #5 $47.61   3.528%   $49.2897   $49.29   $49.30   $49.30  
  Purchase #6 $230.88   12.788%   $260.4049   $260.40   $260.40   $260.40  
  Purchase #7 $60.90   6.117%   $64.6253   $64.63   $64.65   $64.60  
  7 purchase totals = $784.39       $844.1506   $844.15   $844.15   $844.10