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 $106.87   11.520%   $119.1814   $119.18   $119.20   $119.20  
  Purchase #2 $97.36   12.111%   $109.1513   $109.15   $109.15   $109.20  
  Purchase #3 $221.55   12.212%   $248.6057   $248.61   $248.60   $248.60  
  Purchase #4 $151.68   13.228%   $171.7442   $171.74   $171.75   $171.70  
  Purchase #5 $180.45   5.463%   $190.308   $190.31   $190.30   $190.30  
  Purchase #6 $72.32   7.229%   $77.548   $77.55   $77.55   $77.50  
  Purchase #7 $46.74   4.271%   $48.7363   $48.74   $48.75   $48.70  
  7 purchase totals = $876.97       $965.2749   $965.28   $965.30   $965.20