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 $239.50   5.364%   $252.3468   $252.35   $252.35   $252.30  
  Purchase #2 $69.48   11.715%   $77.6196   $77.62   $77.60   $77.60  
  Purchase #3 $74.30   9.280%   $81.195   $81.20   $81.20   $81.20  
  Purchase #4 $60.30   11.706%   $67.3587   $67.36   $67.35   $67.40  
  Purchase #5 $34.29   11.585%   $38.2625   $38.26   $38.25   $38.30  
  Purchase #6 $123.51   10.843%   $136.9022   $136.90   $136.90   $136.90  
  Purchase #7 $76.60   9.221%   $83.6633   $83.66   $83.65   $83.70  
  7 purchase totals = $677.98       $737.3481   $737.35   $737.30   $737.40