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 $49.49   7.468%   $53.1859   $53.19   $53.20   $53.20  
  Purchase #2 $219.93   7.853%   $237.2011   $237.20   $237.20   $237.20  
  Purchase #3 $134.43   9.690%   $147.4563   $147.46   $147.45   $147.50  
  Purchase #4 $69.58   6.262%   $73.9371   $73.94   $73.95   $73.90  
  Purchase #5 $17.57   3.131%   $18.1201   $18.12   $18.10   $18.10  
  Purchase #6 $227.86   4.420%   $237.9314   $237.93   $237.95   $237.90  
  Purchase #7 $124.41   4.643%   $130.1864   $130.19   $130.20   $130.20  
  7 purchase totals = $843.27       $898.0183   $898.03   $898.05   $898.00