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 $61.54   11.611%   $68.6854   $68.69   $68.70   $68.70  
  Purchase #2 $216.81   10.469%   $239.5078   $239.51   $239.50   $239.50  
  Purchase #3 $197.99   5.263%   $208.4102   $208.41   $208.40   $208.40  
  Purchase #4 $83.42   8.236%   $90.2905   $90.29   $90.30   $90.30  
  Purchase #5 $221.77   11.131%   $246.4552   $246.46   $246.45   $246.50  
  Purchase #6 $192.34   7.665%   $207.0829   $207.08   $207.10   $207.10  
  Purchase #7 $176.69   10.504%   $195.2495   $195.25   $195.25   $195.20  
  7 purchase totals = $1,150.56       $1,255.6815   $1,255.69   $1,255.70   $1,255.70