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 $198.33   5.114%   $208.4726   $208.47   $208.45   $208.50  
  Purchase #2 $231.87   12.564%   $261.0021   $261.00   $261.00   $261.00  
  Purchase #3 $222.49   13.727%   $253.0312   $253.03   $253.05   $253.00  
  Purchase #4 $156.53   12.562%   $176.1933   $176.19   $176.20   $176.20  
  Purchase #5 $144.28   13.499%   $163.7564   $163.76   $163.75   $163.80  
  Purchase #6 $210.62   3.281%   $217.5304   $217.53   $217.55   $217.50  
  Purchase #7 $116.99   6.136%   $124.1685   $124.17   $124.15   $124.20  
  7 purchase totals = $1,281.11       $1,404.1545   $1,404.15   $1,404.15   $1,404.20