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 $68.94   10.719%   $76.3297   $76.33   $76.35   $76.30  
  Purchase #2 $24.91   5.416%   $26.2591   $26.26   $26.25   $26.30  
  Purchase #3 $235.80   4.597%   $246.6397   $246.64   $246.65   $246.60  
  Purchase #4 $12.53   3.420%   $12.9585   $12.96   $12.95   $13.00  
  Purchase #5 $182.66   7.351%   $196.0873   $196.09   $196.10   $196.10  
  Purchase #6 $38.25   6.192%   $40.6184   $40.62   $40.60   $40.60  
  Purchase #7 $208.95   3.564%   $216.397   $216.40   $216.40   $216.40  
  7 purchase totals = $772.04       $815.2897   $815.30   $815.30   $815.30