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	$172.65	11.396%	$192.3252	$192.33	$192.35	$192.30
Purchase #2	$250.86	13.489%	$284.6985	$284.70	$284.70	$284.70
Purchase #3	$103.93	9.845%	$114.1619	$114.16	$114.15	$114.20
Purchase #4	$234.85	8.281%	$254.2979	$254.30	$254.30	$254.30
Purchase #5	$123.71	3.195%	$127.6625	$127.66	$127.65	$127.70
Purchase #6	$38.89	9.138%	$42.4438	$42.44	$42.45	$42.40
Purchase #7	$182.56	12.215%	$204.8597	$204.86	$204.85	$204.90
7 purchase totals =	$1,107.45		$1,220.4495	$1,220.45	$1,220.45	$1,220.50