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	$66.78	9.681%	$73.245	$73.25	$73.25	$73.20
Purchase #2	$177.75	10.491%	$196.3978	$196.40	$196.40	$196.40
Purchase #3	$33.50	5.563%	$35.3636	$35.36	$35.35	$35.40
Purchase #4	$124.58	3.724%	$129.2194	$129.22	$129.20	$129.20
Purchase #5	$37.74	6.154%	$40.0625	$40.06	$40.05	$40.10
Purchase #6	$110.93	6.737%	$118.4034	$118.40	$118.40	$118.40
Purchase #7	$35.83	12.105%	$40.1672	$40.17	$40.15	$40.20
7 purchase totals =	$587.11		$632.8589	$632.86	$632.80	$632.90