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 $52.33   7.739%   $56.3798   $56.38   $56.40   $56.40  
  Purchase #2 $236.65   10.565%   $261.6521   $261.65   $261.65   $261.70  
  Purchase #3 $31.72   7.280%   $34.0292   $34.03   $34.05   $34.00  
  Purchase #4 $64.45   3.350%   $66.6091   $66.61   $66.60   $66.60  
  Purchase #5 $201.99   4.109%   $210.2898   $210.29   $210.30   $210.30  
  Purchase #6 $217.42   10.195%   $239.586   $239.59   $239.60   $239.60  
  Purchase #7 $139.57   4.131%   $145.3356   $145.34   $145.35   $145.30  
  7 purchase totals = $944.13       $1,013.8816   $1,013.89   $1,013.95   $1,013.90