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 $244.67   9.141%   $267.0353   $267.04   $267.05   $267.00  
  Purchase #2 $127.39   4.448%   $133.0563   $133.06   $133.05   $133.10  
  Purchase #3 $103.42   10.453%   $114.2305   $114.23   $114.25   $114.20  
  Purchase #4 $187.63   8.591%   $203.7493   $203.75   $203.75   $203.70  
  Purchase #5 $52.65   7.164%   $56.4218   $56.42   $56.40   $56.40  
  Purchase #6 $64.60   6.733%   $68.9495   $68.95   $68.95   $68.90  
  Purchase #7 $86.40   5.235%   $90.923   $90.92   $90.90   $90.90  
  7 purchase totals = $866.76       $934.3657   $934.37   $934.35   $934.20