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 $64.91   4.712%   $67.9686   $67.97   $67.95   $68.00  
  Purchase #2 $213.87   9.346%   $233.8583   $233.86   $233.85   $233.90  
  Purchase #3 $49.65   10.760%   $54.9923   $54.99   $55.00   $55.00  
  Purchase #4 $22.61   3.740%   $23.4556   $23.46   $23.45   $23.50  
  Purchase #5 $95.25   10.256%   $105.0188   $105.02   $105.00   $105.00  
  Purchase #6 $192.60   4.812%   $201.8679   $201.87   $201.85   $201.90  
  Purchase #7 $216.76   9.570%   $237.5039   $237.50   $237.50   $237.50  
  7 purchase totals = $855.65       $924.6654   $924.67   $924.60   $924.80