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 $229.42   8.240%   $248.3242   $248.32   $248.30   $248.30  
  Purchase #2 $219.53   5.566%   $231.749   $231.75   $231.75   $231.70  
  Purchase #3 $89.51   10.441%   $98.8557   $98.86   $98.85   $98.90  
  Purchase #4 $184.78   12.718%   $208.2803   $208.28   $208.30   $208.30  
  Purchase #5 $238.76   11.391%   $265.9572   $265.96   $265.95   $266.00  
  Purchase #6 $63.85   3.335%   $65.9794   $65.98   $66.00   $66.00  
  Purchase #7 $163.68   7.682%   $176.2539   $176.25   $176.25   $176.30  
  7 purchase totals = $1,189.53       $1,295.3997   $1,295.40   $1,295.40   $1,295.50