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	$114.64	12.523%	$128.9964	$129.00	$129.00	$129.00
Purchase #2	$127.53	13.141%	$144.2887	$144.29	$144.30	$144.30
Purchase #3	$31.92	12.309%	$35.849	$35.85	$35.85	$35.80
Purchase #4	$99.78	9.675%	$109.4337	$109.43	$109.45	$109.40
Purchase #5	$60.28	8.137%	$65.185	$65.19	$65.20	$65.20
Purchase #6	$57.65	8.627%	$62.6235	$62.62	$62.60	$62.60
Purchase #7	$109.70	8.237%	$118.736	$118.74	$118.75	$118.70
7 purchase totals =	$601.50		$665.1123	$665.12	$665.15	$665.00