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 $168.93   4.373%   $176.3173   $176.32   $176.30   $176.30  
  Purchase #2 $66.48   6.741%   $70.9614   $70.96   $70.95   $71.00  
  Purchase #3 $146.73   6.662%   $156.5052   $156.51   $156.50   $156.50  
  Purchase #4 $142.56   10.354%   $157.3207   $157.32   $157.30   $157.30  
  Purchase #5 $124.71   4.615%   $130.4654   $130.47   $130.45   $130.50  
  Purchase #6 $214.90   13.130%   $243.1164   $243.12   $243.10   $243.10  
  Purchase #7 $220.87   8.621%   $239.9112   $239.91   $239.90   $239.90  
  7 purchase totals = $1,085.18       $1,174.5976   $1,174.61   $1,174.50   $1,174.60