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 $116.25   8.788%   $126.4661   $126.47   $126.45   $126.50  
  Purchase #2 $224.77   3.245%   $232.0638   $232.06   $232.05   $232.10  
  Purchase #3 $104.61   9.416%   $114.4601   $114.46   $114.45   $114.50  
  Purchase #4 $147.38   11.250%   $163.9603   $163.96   $163.95   $164.00  
  Purchase #5 $227.25   6.111%   $241.1372   $241.14   $241.15   $241.10  
  Purchase #6 $243.43   8.105%   $263.16   $263.16   $263.15   $263.20  
  Purchase #7 $116.31   13.621%   $132.1526   $132.15   $132.15   $132.20  
  7 purchase totals = $1,180.00       $1,273.4001   $1,273.40   $1,273.35   $1,273.60