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	$104.74	6.801%	$111.8634	$111.86	$111.85	$111.90
Purchase #2	$173.39	9.482%	$189.8308	$189.83	$189.85	$189.80
Purchase #3	$179.66	5.538%	$189.6096	$189.61	$189.60	$189.60
Purchase #4	$244.43	12.831%	$275.7928	$275.79	$275.80	$275.80
Purchase #5	$170.62	4.366%	$178.0693	$178.07	$178.05	$178.10
Purchase #6	$59.41	5.457%	$62.652	$62.65	$62.65	$62.70
Purchase #7	$211.61	4.532%	$221.2002	$221.20	$221.20	$221.20
7 purchase totals =	$1,143.86		$1,229.0181	$1,229.01	$1,229.00	$1,229.10