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 $250.32   5.453%   $263.9699   $263.97   $263.95   $264.00  
  Purchase #2 $127.27   12.831%   $143.6   $143.60   $143.60   $143.60  
  Purchase #3 $231.69   7.748%   $249.6413   $249.64   $249.65   $249.60  
  Purchase #4 $135.75   6.546%   $144.6362   $144.64   $144.65   $144.60  
  Purchase #5 $86.79   7.425%   $93.2342   $93.23   $93.25   $93.20  
  Purchase #6 $50.25   5.697%   $53.1127   $53.11   $53.10   $53.10  
  Purchase #7 $108.64   13.624%   $123.4411   $123.44   $123.45   $123.40  
  7 purchase totals = $990.71       $1,071.6354   $1,071.63   $1,071.65   $1,071.50