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 $55.97   11.716%   $62.5274   $62.53   $62.55   $62.50  
  Purchase #2 $46.35   6.217%   $49.2316   $49.23   $49.25   $49.20  
  Purchase #3 $196.90   5.173%   $207.0856   $207.09   $207.10   $207.10  
  Purchase #4 $24.66   11.589%   $27.5178   $27.52   $27.50   $27.50  
  Purchase #5 $28.55   5.565%   $30.1388   $30.14   $30.15   $30.10  
  Purchase #6 $177.47   5.620%   $187.4438   $187.44   $187.45   $187.40  
  Purchase #7 $250.31   7.484%   $269.0432   $269.04   $269.05   $269.00  
  7 purchase totals = $780.21       $832.9882   $832.99   $833.05   $832.80