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 $161.88   13.109%   $183.1008   $183.10   $183.10   $183.10  
  Purchase #2 $220.75   5.384%   $232.6352   $232.64   $232.65   $232.60  
  Purchase #3 $33.66   4.231%   $35.0842   $35.08   $35.10   $35.10  
  Purchase #4 $211.83   10.705%   $234.5064   $234.51   $234.50   $234.50  
  Purchase #5 $44.32   3.798%   $46.0033   $46.00   $46.00   $46.00  
  Purchase #6 $38.87   10.284%   $42.8674   $42.87   $42.85   $42.90  
  Purchase #7 $76.33   6.485%   $81.28   $81.28   $81.30   $81.30  
  7 purchase totals = $787.64       $855.4773   $855.48   $855.50   $855.50