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 $72.36   10.389%   $79.8775   $79.88   $79.90   $79.90  
  Purchase #2 $42.40   3.685%   $43.9624   $43.96   $43.95   $44.00  
  Purchase #3 $188.68   5.394%   $198.8574   $198.86   $198.85   $198.90  
  Purchase #4 $198.83   13.359%   $225.3917   $225.39   $225.40   $225.40  
  Purchase #5 $22.34   3.493%   $23.1203   $23.12   $23.10   $23.10  
  Purchase #6 $122.62   11.170%   $136.3167   $136.32   $136.30   $136.30  
  Purchase #7 $84.32   5.575%   $89.0208   $89.02   $89.00   $89.00  
  7 purchase totals = $731.55       $796.5468   $796.55   $796.50   $796.60