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	$26.43	8.302%	$28.6242	$28.62	$28.60	$28.60
Purchase #2	$75.55	4.363%	$78.8462	$78.85	$78.85	$78.80
Purchase #3	$6.64	9.365%	$7.2618	$7.26	$7.25	$7.30
Purchase #4	$35.39	13.391%	$40.1291	$40.13	$40.15	$40.10
Purchase #5	$173.55	3.863%	$180.2542	$180.25	$180.25	$180.30
Purchase #6	$70.65	7.631%	$76.0413	$76.04	$76.05	$76.00
Purchase #7	$35.86	6.426%	$38.1644	$38.16	$38.15	$38.20
7 purchase totals =	$424.07		$449.3212	$449.31	$449.30	$449.30