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 $101.87   12.727%   $114.835   $114.84   $114.85   $114.80  
  Purchase #2 $232.64   4.228%   $242.476   $242.48   $242.50   $242.50  
  Purchase #3 $248.58   13.155%   $281.2807   $281.28   $281.30   $281.30  
  Purchase #4 $188.77   7.311%   $202.571   $202.57   $202.55   $202.60  
  Purchase #5 $161.74   13.444%   $183.4843   $183.48   $183.50   $183.50  
  Purchase #6 $234.85   13.127%   $265.6788   $265.68   $265.70   $265.70  
  Purchase #7 $249.92   8.123%   $270.221   $270.22   $270.20   $270.20  
  7 purchase totals = $1,418.37       $1,560.5468   $1,560.55   $1,560.60   $1,560.60