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	$180.52	4.630%	$188.8781	$188.88	$188.90	$188.90
Purchase #2	$165.26	7.495%	$177.6462	$177.65	$177.65	$177.60
Purchase #3	$106.29	4.702%	$111.2878	$111.29	$111.30	$111.30
Purchase #4	$88.27	12.831%	$99.5959	$99.60	$99.60	$99.60
Purchase #5	$40.64	5.108%	$42.7159	$42.72	$42.70	$42.70
Purchase #6	$228.78	3.815%	$237.508	$237.51	$237.50	$237.50
Purchase #7	$155.57	9.561%	$170.444	$170.44	$170.45	$170.40
7 purchase totals =	$965.33		$1,028.0759	$1,028.09	$1,028.10	$1,028.00