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 $236.82   8.255%   $256.3695   $256.37   $256.35   $256.40  
  Purchase #2 $65.69   13.536%   $74.5818   $74.58   $74.60   $74.60  
  Purchase #3 $23.55   11.102%   $26.1645   $26.16   $26.15   $26.20  
  Purchase #4 $92.62   11.870%   $103.614   $103.61   $103.60   $103.60  
  Purchase #5 $120.76   8.681%   $131.2432   $131.24   $131.25   $131.20  
  Purchase #6 $6.41   13.671%   $7.2863   $7.29   $7.30   $7.30  
  Purchase #7 $177.99   13.612%   $202.218   $202.22   $202.20   $202.20  
  7 purchase totals = $723.84       $801.4773   $801.47   $801.45   $801.50