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 $186.39   10.541%   $206.0374   $206.04   $206.05   $206.00  
  Purchase #2 $23.29   13.675%   $26.4749   $26.47   $26.45   $26.50  
  Purchase #3 $16.52   12.588%   $18.5995   $18.60   $18.60   $18.60  
  Purchase #4 $167.81   5.337%   $176.766   $176.77   $176.75   $176.80  
  Purchase #5 $239.50   3.790%   $248.5771   $248.58   $248.60   $248.60  
  Purchase #6 $105.85   3.428%   $109.4785   $109.48   $109.50   $109.50  
  Purchase #7 $150.32   9.114%   $164.0202   $164.02   $164.00   $164.00  
  7 purchase totals = $889.68       $949.9536   $949.96   $949.95   $950.00