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 $9.82   11.669%   $10.9659   $10.97   $10.95   $11.00  
  Purchase #2 $59.65   8.841%   $64.9237   $64.92   $64.90   $64.90  
  Purchase #3 $82.83   4.655%   $86.6857   $86.69   $86.70   $86.70  
  Purchase #4 $137.37   11.247%   $152.82   $152.82   $152.80   $152.80  
  Purchase #5 $105.63   5.854%   $111.8136   $111.81   $111.80   $111.80  
  Purchase #6 $50.41   11.551%   $56.2329   $56.23   $56.25   $56.20  
  Purchase #7 $102.78   12.793%   $115.9286   $115.93   $115.95   $115.90  
  7 purchase totals = $548.49       $599.3704   $599.37   $599.35   $599.30