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 $52.79   12.246%   $59.2547   $59.25   $59.25   $59.30  
  Purchase #2 $193.73   8.678%   $210.5419   $210.54   $210.55   $210.50  
  Purchase #3 $53.40   7.260%   $57.2768   $57.28   $57.30   $57.30  
  Purchase #4 $173.77   8.402%   $188.3702   $188.37   $188.35   $188.40  
  Purchase #5 $9.40   6.509%   $10.0118   $10.01   $10.00   $10.00  
  Purchase #6 $250.30   11.743%   $279.6927   $279.69   $279.70   $279.70  
  Purchase #7 $226.34   13.559%   $257.0294   $257.03   $257.05   $257.00  
  7 purchase totals = $959.73       $1,062.1775   $1,062.17   $1,062.20   $1,062.20