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	$125.51	13.609%	$142.5907	$142.59	$142.60	$142.60
Purchase #2	$212.34	5.161%	$223.2989	$223.30	$223.30	$223.30
Purchase #3	$156.68	10.262%	$172.7585	$172.76	$172.75	$172.80
Purchase #4	$59.89	10.551%	$66.209	$66.21	$66.20	$66.20
Purchase #5	$98.55	5.487%	$103.9574	$103.96	$103.95	$104.00
Purchase #6	$50.76	10.438%	$56.0583	$56.06	$56.05	$56.10
Purchase #7	$236.28	8.592%	$256.5812	$256.58	$256.60	$256.60
7 purchase totals =	$940.01		$1,021.4540	$1,021.46	$1,021.45	$1,021.60