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 $50.25   11.649%   $56.1036   $56.10   $56.10   $56.10  
  Purchase #2 $195.97   7.782%   $211.2204   $211.22   $211.20   $211.20  
  Purchase #3 $114.33   11.412%   $127.3773   $127.38   $127.40   $127.40  
  Purchase #4 $31.48   4.669%   $32.9498   $32.95   $32.95   $32.90  
  Purchase #5 $239.82   9.192%   $261.8643   $261.86   $261.85   $261.90  
  Purchase #6 $181.75   6.690%   $193.9091   $193.91   $193.90   $193.90  
  Purchase #7 $42.37   5.311%   $44.6203   $44.62   $44.60   $44.60  
  7 purchase totals = $855.97       $928.0448   $928.04   $928.00   $928.00