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	$101.34	10.141%	$111.6169	$111.62	$111.60	$111.60
Purchase #2	$66.44	5.823%	$70.3088	$70.31	$70.30	$70.30
Purchase #3	$208.89	6.652%	$222.7854	$222.79	$222.80	$222.80
Purchase #4	$84.62	7.409%	$90.8895	$90.89	$90.90	$90.90
Purchase #5	$170.95	8.247%	$185.0482	$185.05	$185.05	$185.00
Purchase #6	$107.82	12.462%	$121.2565	$121.26	$121.25	$121.30
Purchase #7	$34.55	6.374%	$36.7522	$36.75	$36.75	$36.80
7 purchase totals =	$774.61		$838.6575	$838.67	$838.65	$838.70