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	$141.55	11.565%	$157.9203	$157.92	$157.90	$157.90
Purchase #2	$241.70	5.838%	$255.8104	$255.81	$255.80	$255.80
Purchase #3	$147.30	7.606%	$158.5036	$158.50	$158.50	$158.50
Purchase #4	$109.45	6.332%	$116.3804	$116.38	$116.40	$116.40
Purchase #5	$245.49	12.111%	$275.2213	$275.22	$275.20	$275.20
Purchase #6	$50.65	5.710%	$53.5421	$53.54	$53.55	$53.50
Purchase #7	$43.74	12.255%	$49.1003	$49.10	$49.10	$49.10
7 purchase totals =	$979.88		$1,066.4784	$1,066.47	$1,066.45	$1,066.40