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 $55.89   7.386%   $60.018   $60.02   $60.00   $60.00  
  Purchase #2 $156.86   11.716%   $175.2377   $175.24   $175.25   $175.20  
  Purchase #3 $118.41   4.767%   $124.0546   $124.05   $124.05   $124.10  
  Purchase #4 $35.81   11.354%   $39.8759   $39.88   $39.90   $39.90  
  Purchase #5 $182.66   4.397%   $190.6916   $190.69   $190.70   $190.70  
  Purchase #6 $236.83   9.105%   $258.3934   $258.39   $258.40   $258.40  
  Purchase #7 $240.58   13.390%   $272.7937   $272.79   $272.80   $272.80  
  7 purchase totals = $1,027.04       $1,121.0649   $1,121.06   $1,121.10   $1,121.10