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	$108.86	3.423%	$112.5863	$112.59	$112.60	$112.60
Purchase #2	$140.38	13.326%	$159.087	$159.09	$159.10	$159.10
Purchase #3	$52.25	8.459%	$56.6698	$56.67	$56.65	$56.70
Purchase #4	$52.53	3.826%	$54.5398	$54.54	$54.55	$54.50
Purchase #5	$55.93	8.324%	$60.5856	$60.59	$60.60	$60.60
Purchase #6	$167.90	3.123%	$173.1435	$173.14	$173.15	$173.10
Purchase #7	$63.55	12.432%	$71.4505	$71.45	$71.45	$71.50
7 purchase totals =	$641.40		$688.0625	$688.07	$688.10	$688.10