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 $232.38   3.794%   $241.1965   $241.20   $241.20   $241.20  
  Purchase #2 $25.90   7.560%   $27.858   $27.86   $27.85   $27.90  
  Purchase #3 $22.43   13.249%   $25.4018   $25.40   $25.40   $25.40  
  Purchase #4 $218.85   13.382%   $248.1365   $248.14   $248.15   $248.10  
  Purchase #5 $129.86   5.543%   $137.0581   $137.06   $137.05   $137.10  
  Purchase #6 $202.46   5.508%   $213.6115   $213.61   $213.60   $213.60  
  Purchase #7 $127.53   6.253%   $135.5045   $135.50   $135.50   $135.50  
  7 purchase totals = $959.41       $1,028.7669   $1,028.77   $1,028.75   $1,028.80