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 $242.59   11.117%   $269.5587   $269.56   $269.55   $269.60  
  Purchase #2 $50.92   4.287%   $53.1029   $53.10   $53.10   $53.10  
  Purchase #3 $62.46   3.829%   $64.8516   $64.85   $64.85   $64.90  
  Purchase #4 $82.95   4.872%   $86.9913   $86.99   $87.00   $87.00  
  Purchase #5 $76.92   3.358%   $79.503   $79.50   $79.50   $79.50  
  Purchase #6 $24.87   3.602%   $25.7658   $25.77   $25.75   $25.80  
  Purchase #7 $207.32   4.671%   $217.0039   $217.00   $217.00   $217.00  
  7 purchase totals = $748.03       $796.7772   $796.77   $796.75   $796.90