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 $52.91   13.661%   $60.138   $60.14   $60.15   $60.10  
  Purchase #2 $54.55   3.415%   $56.4129   $56.41   $56.40   $56.40  
  Purchase #3 $83.41   10.608%   $92.2581   $92.26   $92.25   $92.30  
  Purchase #4 $62.78   6.563%   $66.9003   $66.90   $66.90   $66.90  
  Purchase #5 $226.89   9.675%   $248.8416   $248.84   $248.85   $248.80  
  Purchase #6 $8.62   10.252%   $9.5037   $9.50   $9.50   $9.50  
  Purchase #7 $153.38   6.129%   $162.7807   $162.78   $162.80   $162.80  
  7 purchase totals = $642.54       $696.8353   $696.83   $696.85   $696.80