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 $207.47   12.763%   $233.9494   $233.95   $233.95   $233.90  
  Purchase #2 $249.40   3.679%   $258.5754   $258.58   $258.60   $258.60  
  Purchase #3 $165.88   9.813%   $182.1578   $182.16   $182.15   $182.20  
  Purchase #4 $185.35   4.248%   $193.2237   $193.22   $193.20   $193.20  
  Purchase #5 $174.66   6.742%   $186.4356   $186.44   $186.45   $186.40  
  Purchase #6 $62.65   4.799%   $65.6566   $65.66   $65.65   $65.70  
  Purchase #7 $125.89   7.452%   $135.2713   $135.27   $135.25   $135.30  
  7 purchase totals = $1,171.30       $1,255.2698   $1,255.28   $1,255.25   $1,255.30