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 $73.37   10.281%   $80.9132   $80.91   $80.90   $80.90  
  Purchase #2 $60.83   3.487%   $62.9511   $62.95   $62.95   $63.00  
  Purchase #3 $70.79   13.142%   $80.0932   $80.09   $80.10   $80.10  
  Purchase #4 $190.63   9.326%   $208.4082   $208.41   $208.40   $208.40  
  Purchase #5 $185.93   3.243%   $191.9597   $191.96   $191.95   $192.00  
  Purchase #6 $203.71   9.128%   $222.3046   $222.30   $222.30   $222.30  
  Purchase #7 $110.76   4.662%   $115.9236   $115.92   $115.90   $115.90  
  7 purchase totals = $896.02       $962.5536   $962.54   $962.50   $962.60