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 $23.96   10.774%   $26.5415   $26.54   $26.55   $26.50  
  Purchase #2 $245.48   3.614%   $254.3516   $254.35   $254.35   $254.40  
  Purchase #3 $33.89   6.487%   $36.0884   $36.09   $36.10   $36.10  
  Purchase #4 $61.53   13.391%   $69.7695   $69.77   $69.75   $69.80  
  Purchase #5 $124.81   12.814%   $140.8032   $140.80   $140.80   $140.80  
  Purchase #6 $239.69   5.629%   $253.1822   $253.18   $253.20   $253.20  
  Purchase #7 $228.58   6.335%   $243.0605   $243.06   $243.05   $243.10  
  7 purchase totals = $957.94       $1,023.7969   $1,023.79   $1,023.80   $1,023.90