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 $176.97   9.255%   $193.3486   $193.35   $193.35   $193.30  
  Purchase #2 $106.49   7.541%   $114.5204   $114.52   $114.50   $114.50  
  Purchase #3 $178.63   5.739%   $188.8816   $188.88   $188.90   $188.90  
  Purchase #4 $199.79   5.716%   $211.21   $211.21   $211.20   $211.20  
  Purchase #5 $114.99   5.721%   $121.5686   $121.57   $121.55   $121.60  
  Purchase #6 $122.41   3.126%   $126.2365   $126.24   $126.25   $126.20  
  Purchase #7 $79.42   10.167%   $87.4946   $87.49   $87.50   $87.50  
  7 purchase totals = $978.70       $1,043.2603   $1,043.26   $1,043.25   $1,043.20