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 $163.81   8.404%   $177.5766   $177.58   $177.60   $177.60  
  Purchase #2 $223.55   11.253%   $248.7061   $248.71   $248.70   $248.70  
  Purchase #3 $143.25   6.613%   $152.7231   $152.72   $152.70   $152.70  
  Purchase #4 $106.85   11.834%   $119.4946   $119.49   $119.50   $119.50  
  Purchase #5 $14.30   8.385%   $15.4991   $15.50   $15.50   $15.50  
  Purchase #6 $98.61   9.335%   $107.8152   $107.82   $107.80   $107.80  
  Purchase #7 $143.67   6.380%   $152.8361   $152.84   $152.85   $152.80  
  7 purchase totals = $894.04       $974.6508   $974.66   $974.65   $974.60