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 $155.62   11.780%   $173.952   $173.95   $173.95   $174.00  
  Purchase #2 $68.83   12.733%   $77.5941   $77.59   $77.60   $77.60  
  Purchase #3 $200.48   3.743%   $207.984   $207.98   $208.00   $208.00  
  Purchase #4 $194.69   13.643%   $221.2516   $221.25   $221.25   $221.30  
  Purchase #5 $199.77   7.119%   $213.9916   $213.99   $214.00   $214.00  
  Purchase #6 $245.89   6.829%   $262.6818   $262.68   $262.70   $262.70  
  Purchase #7 $216.37   9.513%   $236.9533   $236.95   $236.95   $237.00  
  7 purchase totals = $1,281.65       $1,394.4084   $1,394.39   $1,394.45   $1,394.60