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 $82.32   5.237%   $86.6311   $86.63   $86.65   $86.60  
  Purchase #2 $185.67   11.685%   $207.3655   $207.37   $207.35   $207.40  
  Purchase #3 $248.68   11.312%   $276.8107   $276.81   $276.80   $276.80  
  Purchase #4 $105.69   7.243%   $113.3451   $113.35   $113.35   $113.30  
  Purchase #5 $214.43   13.856%   $244.1414   $244.14   $244.15   $244.10  
  Purchase #6 $171.71   12.847%   $193.7696   $193.77   $193.75   $193.80  
  Purchase #7 $205.75   4.213%   $214.4182   $214.42   $214.40   $214.40  
  7 purchase totals = $1,214.25       $1,336.4816   $1,336.49   $1,336.45   $1,336.40