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	$76.74	8.815%	$83.5046	$83.50	$83.50	$83.50
Purchase #2	$40.60	4.688%	$42.5033	$42.50	$42.50	$42.50
Purchase #3	$82.51	11.526%	$92.0201	$92.02	$92.00	$92.00
Purchase #4	$107.65	6.387%	$114.5256	$114.53	$114.55	$114.50
Purchase #5	$111.45	5.353%	$117.4159	$117.42	$117.40	$117.40
Purchase #6	$47.92	6.183%	$50.8829	$50.88	$50.90	$50.90
Purchase #7	$80.75	12.820%	$91.1022	$91.10	$91.10	$91.10
7 purchase totals =	$547.62		$591.9546	$591.95	$591.95	$591.90