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 $115.83   9.848%   $127.2369   $127.24   $127.25   $127.20  
  Purchase #2 $140.68   11.343%   $156.6373   $156.64   $156.65   $156.60  
  Purchase #3 $11.51   4.585%   $12.0377   $12.04   $12.05   $12.00  
  Purchase #4 $218.60   8.853%   $237.9527   $237.95   $237.95   $238.00  
  Purchase #5 $89.88   7.565%   $96.6794   $96.68   $96.70   $96.70  
  Purchase #6 $146.54   7.116%   $156.9678   $156.97   $156.95   $157.00  
  Purchase #7 $159.42   10.807%   $176.6485   $176.65   $176.65   $176.60  
  7 purchase totals = $882.46       $964.1603   $964.17   $964.20   $964.10