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 $161.96   5.874%   $171.4735   $171.47   $171.45   $171.50  
  Purchase #2 $39.99   7.291%   $42.9057   $42.91   $42.90   $42.90  
  Purchase #3 $49.35   4.317%   $51.4804   $51.48   $51.50   $51.50  
  Purchase #4 $54.73   5.275%   $57.617   $57.62   $57.60   $57.60  
  Purchase #5 $83.97   13.252%   $95.0977   $95.10   $95.10   $95.10  
  Purchase #6 $67.35   13.419%   $76.3877   $76.39   $76.40   $76.40  
  Purchase #7 $202.61   5.602%   $213.9602   $213.96   $213.95   $214.00  
  7 purchase totals = $659.96       $708.9222   $708.93   $708.90   $709.00