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 $239.68   8.435%   $259.897   $259.90   $259.90   $259.90  
  Purchase #2 $46.68   3.346%   $48.2419   $48.24   $48.25   $48.20  
  Purchase #3 $47.72   3.708%   $49.4895   $49.49   $49.50   $49.50  
  Purchase #4 $227.62   7.575%   $244.8622   $244.86   $244.85   $244.90  
  Purchase #5 $75.29   6.147%   $79.9181   $79.92   $79.90   $79.90  
  Purchase #6 $50.65   3.597%   $52.4719   $52.47   $52.45   $52.50  
  Purchase #7 $28.61   8.217%   $30.9609   $30.96   $30.95   $31.00  
  7 purchase totals = $716.25       $765.8415   $765.84   $765.80   $765.90