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 $22.88   13.793%   $26.0358   $26.04   $26.05   $26.00  
  Purchase #2 $119.51   7.733%   $128.7517   $128.75   $128.75   $128.80  
  Purchase #3 $144.60   10.271%   $159.4519   $159.45   $159.45   $159.50  
  Purchase #4 $117.56   13.766%   $133.7433   $133.74   $133.75   $133.70  
  Purchase #5 $74.26   13.505%   $84.2888   $84.29   $84.30   $84.30  
  Purchase #6 $73.45   4.861%   $77.0204   $77.02   $77.00   $77.00  
  Purchase #7 $184.44   6.325%   $196.1058   $196.11   $196.10   $196.10  
  7 purchase totals = $736.70       $805.3977   $805.40   $805.40   $805.40