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 $42.48   4.260%   $44.2896   $44.29   $44.30   $44.30  
  Purchase #2 $161.34   10.431%   $178.1694   $178.17   $178.15   $178.20  
  Purchase #3 $179.53   3.806%   $186.3629   $186.36   $186.35   $186.40  
  Purchase #4 $208.55   12.725%   $235.088   $235.09   $235.10   $235.10  
  Purchase #5 $71.28   4.613%   $74.5681   $74.57   $74.55   $74.60  
  Purchase #6 $206.55   13.486%   $234.4053   $234.41   $234.40   $234.40  
  Purchase #7 $159.36   4.175%   $166.0133   $166.01   $166.00   $166.00  
  7 purchase totals = $1,029.09       $1,118.8966   $1,118.90   $1,118.85   $1,119.00