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 $104.77   11.166%   $116.4686   $116.47   $116.45   $116.50  
  Purchase #2 $189.65   9.651%   $207.9531   $207.95   $207.95   $208.00  
  Purchase #3 $42.47   8.597%   $46.1211   $46.12   $46.10   $46.10  
  Purchase #4 $162.44   12.815%   $183.2567   $183.26   $183.25   $183.30  
  Purchase #5 $42.87   3.277%   $44.2748   $44.27   $44.25   $44.30  
  Purchase #6 $114.72   11.159%   $127.5216   $127.52   $127.50   $127.50  
  Purchase #7 $169.49   6.818%   $181.0458   $181.05   $181.05   $181.00  
  7 purchase totals = $826.41       $906.6417   $906.64   $906.55   $906.70