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 $53.78   11.641%   $60.0405   $60.04   $60.05   $60.00  
  Purchase #2 $178.95   13.141%   $202.4658   $202.47   $202.45   $202.50  
  Purchase #3 $77.27   11.360%   $86.0479   $86.05   $86.05   $86.00  
  Purchase #4 $85.83   5.546%   $90.5901   $90.59   $90.60   $90.60  
  Purchase #5 $14.58   9.610%   $15.9811   $15.98   $16.00   $16.00  
  Purchase #6 $242.69   9.243%   $265.1218   $265.12   $265.10   $265.10  
  Purchase #7 $154.53   6.682%   $164.8557   $164.86   $164.85   $164.90  
  7 purchase totals = $807.63       $885.1029   $885.11   $885.10   $885.10