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 $68.83   13.347%   $78.0167   $78.02   $78.00   $78.00  
  Purchase #2 $40.43   8.725%   $43.9575   $43.96   $43.95   $44.00  
  Purchase #3 $29.81   13.391%   $33.8019   $33.80   $33.80   $33.80  
  Purchase #4 $26.99   10.648%   $29.8639   $29.86   $29.85   $29.90  
  Purchase #5 $125.80   8.812%   $136.8855   $136.89   $136.90   $136.90  
  Purchase #6 $30.71   7.839%   $33.1174   $33.12   $33.10   $33.10  
  Purchase #7 $202.35   8.196%   $218.9346   $218.93   $218.95   $218.90  
  7 purchase totals = $524.92       $574.5775   $574.58   $574.55   $574.60