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 $233.45   12.479%   $262.5822   $262.58   $262.60   $262.60  
  Purchase #2 $176.93   8.589%   $192.1265   $192.13   $192.15   $192.10  
  Purchase #3 $92.95   6.217%   $98.7287   $98.73   $98.75   $98.70  
  Purchase #4 $93.51   8.224%   $101.2003   $101.20   $101.20   $101.20  
  Purchase #5 $210.61   8.509%   $228.5308   $228.53   $228.55   $228.50  
  Purchase #6 $184.91   13.869%   $210.5552   $210.56   $210.55   $210.60  
  Purchase #7 $94.71   8.127%   $102.4071   $102.41   $102.40   $102.40  
  7 purchase totals = $1,087.07       $1,196.1308   $1,196.14   $1,196.20   $1,196.10