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 $173.94   6.225%   $184.7678   $184.77   $184.75   $184.80  
  Purchase #2 $162.49   9.521%   $177.9607   $177.96   $177.95   $178.00  
  Purchase #3 $250.33   4.268%   $261.0141   $261.01   $261.00   $261.00  
  Purchase #4 $161.58   13.603%   $183.5597   $183.56   $183.55   $183.60  
  Purchase #5 $112.97   12.213%   $126.767   $126.77   $126.75   $126.80  
  Purchase #6 $231.85   13.188%   $262.4264   $262.43   $262.45   $262.40  
  Purchase #7 $78.43   3.491%   $81.168   $81.17   $81.15   $81.20  
  7 purchase totals = $1,171.59       $1,277.6637   $1,277.67   $1,277.60   $1,277.80