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 $46.95   7.462%   $50.4534   $50.45   $50.45   $50.50  
  Purchase #2 $168.60   4.782%   $176.6625   $176.66   $176.65   $176.70  
  Purchase #3 $215.35   5.382%   $226.9401   $226.94   $226.95   $226.90  
  Purchase #4 $60.86   5.113%   $63.9718   $63.97   $63.95   $64.00  
  Purchase #5 $8.66   6.721%   $9.242   $9.24   $9.25   $9.20  
  Purchase #6 $148.79   11.285%   $165.581   $165.58   $165.60   $165.60  
  Purchase #7 $69.35   8.680%   $75.3696   $75.37   $75.35   $75.40  
  7 purchase totals = $718.56       $768.2204   $768.21   $768.20   $768.30