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 $192.74   8.195%   $208.535   $208.54   $208.55   $208.50  
  Purchase #2 $119.96   9.331%   $131.1535   $131.15   $131.15   $131.20  
  Purchase #3 $72.96   6.862%   $77.9665   $77.97   $77.95   $78.00  
  Purchase #4 $52.81   9.257%   $57.6986   $57.70   $57.70   $57.70  
  Purchase #5 $205.35   7.440%   $220.628   $220.63   $220.65   $220.60  
  Purchase #6 $28.61   13.546%   $32.4855   $32.49   $32.50   $32.50  
  Purchase #7 $228.28   10.606%   $252.4914   $252.49   $252.50   $252.50  
  7 purchase totals = $900.71       $980.9585   $980.97   $981.00   $981.00