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 $218.71   13.827%   $248.951   $248.95   $248.95   $249.00  
  Purchase #2 $222.87   9.462%   $243.958   $243.96   $243.95   $244.00  
  Purchase #3 $221.39   6.760%   $236.356   $236.36   $236.35   $236.40  
  Purchase #4 $176.95   8.631%   $192.2226   $192.22   $192.20   $192.20  
  Purchase #5 $94.73   9.299%   $103.5389   $103.54   $103.55   $103.50  
  Purchase #6 $171.63   5.311%   $180.7453   $180.75   $180.75   $180.70  
  Purchase #7 $144.55   7.181%   $154.9301   $154.93   $154.95   $154.90  
  7 purchase totals = $1,250.83       $1,360.7019   $1,360.71   $1,360.70   $1,360.70