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 $57.76   6.639%   $61.5947   $61.59   $61.60   $61.60  
  Purchase #2 $115.68   3.164%   $119.3401   $119.34   $119.35   $119.30  
  Purchase #3 $147.92   9.297%   $161.6721   $161.67   $161.65   $161.70  
  Purchase #4 $198.70   4.784%   $208.2058   $208.21   $208.20   $208.20  
  Purchase #5 $108.63   4.768%   $113.8095   $113.81   $113.80   $113.80  
  Purchase #6 $7.80   9.481%   $8.5395   $8.54   $8.55   $8.50  
  Purchase #7 $82.61   4.223%   $86.0986   $86.10   $86.10   $86.10  
  7 purchase totals = $719.10       $759.2603   $759.26   $759.25   $759.20