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	$230.65	10.863%	$255.7055	$255.71	$255.70	$255.70
Purchase #2	$120.32	7.211%	$128.9963	$129.00	$129.00	$129.00
Purchase #3	$123.75	3.223%	$127.7385	$127.74	$127.75	$127.70
Purchase #4	$106.71	12.752%	$120.3177	$120.32	$120.30	$120.30
Purchase #5	$138.39	9.737%	$151.865	$151.87	$151.85	$151.90
Purchase #6	$192.39	11.321%	$214.1705	$214.17	$214.15	$214.20
Purchase #7	$33.51	13.564%	$38.0553	$38.06	$38.05	$38.10
7 purchase totals =	$945.72		$1,036.8488	$1,036.87	$1,036.80	$1,036.90