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 $234.77   9.577%   $257.2539   $257.25   $257.25   $257.30  
  Purchase #2 $87.35   4.186%   $91.0065   $91.01   $91.00   $91.00  
  Purchase #3 $200.78   9.553%   $219.9605   $219.96   $219.95   $220.00  
  Purchase #4 $26.68   13.318%   $30.2332   $30.23   $30.25   $30.20  
  Purchase #5 $73.84   3.683%   $76.5595   $76.56   $76.55   $76.60  
  Purchase #6 $74.96   9.687%   $82.2214   $82.22   $82.20   $82.20  
  Purchase #7 $27.55   4.333%   $28.7437   $28.74   $28.75   $28.70  
  7 purchase totals = $725.93       $785.9787   $785.97   $785.95   $786.00