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 $26.98   8.400%   $29.2463   $29.25   $29.25   $29.20  
  Purchase #2 $214.35   4.717%   $224.4609   $224.46   $224.45   $224.50  
  Purchase #3 $157.64   12.266%   $176.9761   $176.98   $177.00   $177.00  
  Purchase #4 $108.81   9.615%   $119.2721   $119.27   $119.25   $119.30  
  Purchase #5 $240.97   10.611%   $266.5393   $266.54   $266.55   $266.50  
  Purchase #6 $86.49   11.703%   $96.6119   $96.61   $96.60   $96.60  
  Purchase #7 $160.32   7.326%   $172.065   $172.07   $172.05   $172.10  
  7 purchase totals = $995.56       $1,085.1716   $1,085.18   $1,085.15   $1,085.20