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 $249.47   4.693%   $261.1776   $261.18   $261.20   $261.20  
  Purchase #2 $168.85   4.590%   $176.6002   $176.60   $176.60   $176.60  
  Purchase #3 $48.98   12.570%   $55.1368   $55.14   $55.15   $55.10  
  Purchase #4 $248.90   9.246%   $271.9133   $271.91   $271.90   $271.90  
  Purchase #5 $83.58   3.572%   $86.5655   $86.57   $86.55   $86.60  
  Purchase #6 $91.67   13.130%   $103.7063   $103.71   $103.70   $103.70  
  Purchase #7 $103.68   12.785%   $116.9355   $116.94   $116.95   $116.90  
  7 purchase totals = $995.13       $1,072.0352   $1,072.05   $1,072.05   $1,072.00