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 $90.69   8.795%   $98.6662   $98.67   $98.65   $98.70  
  Purchase #2 $181.65   6.750%   $193.9114   $193.91   $193.90   $193.90  
  Purchase #3 $114.55   8.314%   $124.0737   $124.07   $124.05   $124.10  
  Purchase #4 $183.43   13.694%   $208.5489   $208.55   $208.55   $208.50  
  Purchase #5 $190.81   13.523%   $216.6132   $216.61   $216.60   $216.60  
  Purchase #6 $118.58   4.852%   $124.3335   $124.33   $124.35   $124.30  
  Purchase #7 $148.76   7.228%   $159.5124   $159.51   $159.50   $159.50  
  7 purchase totals = $1,028.47       $1,125.6593   $1,125.65   $1,125.60   $1,125.60