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 $66.94   4.531%   $69.9731   $69.97   $69.95   $70.00  
  Purchase #2 $199.86   4.386%   $208.6259   $208.63   $208.65   $208.60  
  Purchase #3 $114.90   13.694%   $130.6344   $130.63   $130.65   $130.60  
  Purchase #4 $237.85   4.610%   $248.8149   $248.81   $248.80   $248.80  
  Purchase #5 $189.37   9.527%   $207.4113   $207.41   $207.40   $207.40  
  Purchase #6 $231.91   9.444%   $253.8116   $253.81   $253.80   $253.80  
  Purchase #7 $66.63   8.173%   $72.0757   $72.08   $72.10   $72.10  
  7 purchase totals = $1,107.46       $1,191.3469   $1,191.34   $1,191.35   $1,191.30