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 $71.47   3.420%   $73.9143   $73.91   $73.90   $73.90  
  Purchase #2 $82.81   4.853%   $86.8288   $86.83   $86.85   $86.80  
  Purchase #3 $154.34   7.649%   $166.1455   $166.15   $166.15   $166.10  
  Purchase #4 $233.59   12.753%   $263.3797   $263.38   $263.40   $263.40  
  Purchase #5 $121.84   8.384%   $132.0551   $132.06   $132.05   $132.10  
  Purchase #6 $247.65   10.509%   $273.6755   $273.68   $273.70   $273.70  
  Purchase #7 $114.69   12.391%   $128.9012   $128.90   $128.90   $128.90  
  7 purchase totals = $1,026.39       $1,124.9001   $1,124.91   $1,124.95   $1,124.90