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 $87.38   6.464%   $93.0282   $93.03   $93.05   $93.00  
  Purchase #2 $175.41   5.104%   $184.3629   $184.36   $184.35   $184.40  
  Purchase #3 $153.49   12.691%   $172.9694   $172.97   $172.95   $173.00  
  Purchase #4 $26.46   13.758%   $30.1004   $30.10   $30.10   $30.10  
  Purchase #5 $51.32   9.123%   $56.0019   $56.00   $56.00   $56.00  
  Purchase #6 $192.25   10.195%   $211.8499   $211.85   $211.85   $211.80  
  Purchase #7 $110.97   7.477%   $119.2672   $119.27   $119.25   $119.30  
  7 purchase totals = $797.28       $867.5799   $867.58   $867.55   $867.60