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	$21.38	13.520%	$24.2706	$24.27	$24.25	$24.30
Purchase #2	$192.46	12.785%	$217.066	$217.07	$217.05	$217.10
Purchase #3	$71.31	10.319%	$78.6685	$78.67	$78.65	$78.70
Purchase #4	$210.56	9.397%	$230.3463	$230.35	$230.35	$230.30
Purchase #5	$171.37	3.841%	$177.9523	$177.95	$177.95	$178.00
Purchase #6	$17.31	12.796%	$19.525	$19.53	$19.55	$19.50
Purchase #7	$166.44	11.455%	$185.5057	$185.51	$185.50	$185.50
7 purchase totals =	$850.83		$933.3344	$933.35	$933.30	$933.40