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	$154.71	3.215%	$159.6839	$159.68	$159.70	$159.70
Purchase #2	$226.30	5.563%	$238.8891	$238.89	$238.90	$238.90
Purchase #3	$160.73	12.755%	$181.2311	$181.23	$181.25	$181.20
Purchase #4	$42.86	6.422%	$45.6125	$45.61	$45.60	$45.60
Purchase #5	$90.71	9.530%	$99.3547	$99.35	$99.35	$99.40
Purchase #6	$17.61	8.755%	$19.1518	$19.15	$19.15	$19.20
Purchase #7	$173.91	13.290%	$197.0226	$197.02	$197.00	$197.00
7 purchase totals =	$866.83		$940.9457	$940.93	$940.95	$941.00