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 $200.97   11.558%   $224.1981   $224.20   $224.20   $224.20  
  Purchase #2 $169.93   12.255%   $190.7549   $190.75   $190.75   $190.80  
  Purchase #3 $47.28   8.473%   $51.286   $51.29   $51.30   $51.30  
  Purchase #4 $176.99   13.792%   $201.4005   $201.40   $201.40   $201.40  
  Purchase #5 $168.73   4.763%   $176.7666   $176.77   $176.75   $176.80  
  Purchase #6 $149.57   5.798%   $158.2421   $158.24   $158.25   $158.20  
  Purchase #7 $85.60   4.105%   $89.1139   $89.11   $89.10   $89.10  
  7 purchase totals = $999.07       $1,091.7621   $1,091.76   $1,091.75   $1,091.80