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 $183.87   12.413%   $206.6938   $206.69   $206.70   $206.70  
  Purchase #2 $246.90   12.335%   $277.3551   $277.36   $277.35   $277.40  
  Purchase #3 $186.67   13.787%   $212.4062   $212.41   $212.40   $212.40  
  Purchase #4 $32.39   3.244%   $33.4407   $33.44   $33.45   $33.40  
  Purchase #5 $109.68   13.670%   $124.6733   $124.67   $124.65   $124.70  
  Purchase #6 $192.77   9.550%   $211.1795   $211.18   $211.20   $211.20  
  Purchase #7 $222.46   3.246%   $229.6811   $229.68   $229.70   $229.70  
  7 purchase totals = $1,174.74       $1,295.4297   $1,295.43   $1,295.45   $1,295.50