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 $86.54   13.469%   $98.1961   $98.20   $98.20   $98.20  
  Purchase #2 $239.70   8.259%   $259.4968   $259.50   $259.50   $259.50  
  Purchase #3 $153.76   13.400%   $174.3638   $174.36   $174.35   $174.40  
  Purchase #4 $81.72   5.394%   $86.128   $86.13   $86.15   $86.10  
  Purchase #5 $235.95   8.603%   $256.2488   $256.25   $256.25   $256.20  
  Purchase #6 $202.44   5.564%   $213.7038   $213.70   $213.70   $213.70  
  Purchase #7 $121.45   10.440%   $134.1294   $134.13   $134.15   $134.10  
  7 purchase totals = $1,121.56       $1,222.2667   $1,222.27   $1,222.30   $1,222.20