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	$17.66	4.783%	$18.5047	$18.50	$18.50	$18.50
Purchase #2	$189.67	11.335%	$211.1691	$211.17	$211.15	$211.20
Purchase #3	$64.98	13.244%	$73.586	$73.59	$73.60	$73.60
Purchase #4	$33.91	5.616%	$35.8144	$35.81	$35.80	$35.80
Purchase #5	$145.31	7.783%	$156.6195	$156.62	$156.60	$156.60
Purchase #6	$35.80	11.191%	$39.8064	$39.81	$39.80	$39.80
Purchase #7	$135.71	5.477%	$143.1428	$143.14	$143.15	$143.10
7 purchase totals =	$623.04		$678.6429	$678.64	$678.60	$678.60