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	$70.67	10.141%	$77.8366	$77.84	$77.85	$77.80
Purchase #2	$104.52	6.290%	$111.0943	$111.09	$111.10	$111.10
Purchase #3	$232.94	13.382%	$264.112	$264.11	$264.10	$264.10
Purchase #4	$218.26	5.664%	$230.6222	$230.62	$230.60	$230.60
Purchase #5	$244.57	13.672%	$278.0076	$278.01	$278.00	$278.00
Purchase #6	$122.46	3.183%	$126.3579	$126.36	$126.35	$126.40
Purchase #7	$57.70	3.758%	$59.8684	$59.87	$59.85	$59.90
7 purchase totals =	$1,051.12		$1,147.8990	$1,147.90	$1,147.85	$1,147.90