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 $164.43   9.233%   $179.6118   $179.61   $179.60   $179.60  
  Purchase #2 $24.95   6.258%   $26.5114   $26.51   $26.50   $26.50  
  Purchase #3 $240.25   9.516%   $263.1122   $263.11   $263.10   $263.10  
  Purchase #4 $151.67   10.765%   $167.9973   $168.00   $168.00   $168.00  
  Purchase #5 $119.88   13.218%   $135.7257   $135.73   $135.75   $135.70  
  Purchase #6 $241.44   8.664%   $262.3584   $262.36   $262.35   $262.40  
  Purchase #7 $127.50   3.226%   $131.6132   $131.61   $131.60   $131.60  
  7 purchase totals = $1,070.12       $1,166.9300   $1,166.93   $1,166.90   $1,166.90