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	$90.69	10.603%	$100.3059	$100.31	$100.30	$100.30
Purchase #2	$79.50	5.188%	$83.6245	$83.62	$83.60	$83.60
Purchase #3	$91.35	8.803%	$99.3915	$99.39	$99.40	$99.40
Purchase #4	$172.37	7.697%	$185.6373	$185.64	$185.65	$185.60
Purchase #5	$84.58	5.523%	$89.2514	$89.25	$89.25	$89.30
Purchase #6	$125.83	6.604%	$134.1398	$134.14	$134.15	$134.10
Purchase #7	$35.37	12.233%	$39.6968	$39.70	$39.70	$39.70
7 purchase totals =	$679.69		$732.0472	$732.05	$732.05	$732.00