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	$122.64	12.478%	$137.943	$137.94	$137.95	$137.90
Purchase #2	$101.91	9.172%	$111.2572	$111.26	$111.25	$111.30
Purchase #3	$147.32	4.585%	$154.0746	$154.07	$154.05	$154.10
Purchase #4	$71.61	11.827%	$80.0793	$80.08	$80.10	$80.10
Purchase #5	$20.28	5.860%	$21.4684	$21.47	$21.45	$21.50
Purchase #6	$142.86	9.506%	$156.4403	$156.44	$156.45	$156.40
Purchase #7	$19.87	9.233%	$21.7046	$21.70	$21.70	$21.70
7 purchase totals =	$626.49		$682.9674	$682.96	$682.95	$683.00