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	$34.46	12.356%	$38.7179	$38.72	$38.70	$38.70
Purchase #2	$165.52	3.781%	$171.7783	$171.78	$171.80	$171.80
Purchase #3	$16.68	12.346%	$18.7393	$18.74	$18.75	$18.70
Purchase #4	$172.92	9.651%	$189.6085	$189.61	$189.60	$189.60
Purchase #5	$111.91	13.538%	$127.0604	$127.06	$127.05	$127.10
Purchase #6	$205.83	8.712%	$223.7619	$223.76	$223.75	$223.80
Purchase #7	$120.52	7.382%	$129.4168	$129.42	$129.40	$129.40
7 purchase totals =	$827.84		$899.0831	$899.09	$899.05	$899.10