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 $164.80   8.724%   $179.1772   $179.18   $179.20   $179.20  
  Purchase #2 $83.90   10.471%   $92.6852   $92.69   $92.70   $92.70  
  Purchase #3 $226.69   3.848%   $235.413   $235.41   $235.40   $235.40  
  Purchase #4 $180.25   8.612%   $195.7731   $195.77   $195.75   $195.80  
  Purchase #5 $238.77   4.254%   $248.9273   $248.93   $248.95   $248.90  
  Purchase #6 $150.95   8.247%   $163.3988   $163.40   $163.40   $163.40  
  Purchase #7 $83.29   9.784%   $91.4391   $91.44   $91.45   $91.40  
  7 purchase totals = $1,128.65       $1,206.8137   $1,206.82   $1,206.85   $1,206.80