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 $54.77   3.395%   $56.6294   $56.63   $56.65   $56.60  
  Purchase #2 $243.41   8.859%   $264.9737   $264.97   $264.95   $265.00  
  Purchase #3 $5.95   4.308%   $6.2063   $6.21   $6.20   $6.20  
  Purchase #4 $68.70   4.360%   $71.6953   $71.70   $71.70   $71.70  
  Purchase #5 $218.45   3.670%   $226.4671   $226.47   $226.45   $226.50  
  Purchase #6 $105.45   8.480%   $114.3922   $114.39   $114.40   $114.40  
  Purchase #7 $194.96   13.528%   $221.3342   $221.33   $221.35   $221.30  
  7 purchase totals = $891.69       $961.6982   $961.70   $961.70   $961.70