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	$143.37	10.201%	$157.9952	$158.00	$158.00	$158.00
Purchase #2	$53.50	11.123%	$59.4508	$59.45	$59.45	$59.50
Purchase #3	$228.55	5.703%	$241.5842	$241.58	$241.60	$241.60
Purchase #4	$48.74	11.579%	$54.3836	$54.38	$54.40	$54.40
Purchase #5	$152.94	7.668%	$164.6674	$164.67	$164.65	$164.70
Purchase #6	$121.92	4.865%	$127.8514	$127.85	$127.85	$127.90
Purchase #7	$30.44	13.444%	$34.5324	$34.53	$34.55	$34.50
7 purchase totals =	$779.46		$840.4650	$840.46	$840.50	$840.60