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	$28.48	11.530%	$31.7637	$31.76	$31.75	$31.80
Purchase #2	$235.83	12.469%	$265.2356	$265.24	$265.25	$265.20
Purchase #3	$242.45	8.102%	$262.0933	$262.09	$262.10	$262.10
Purchase #4	$157.82	9.309%	$172.5115	$172.51	$172.50	$172.50
Purchase #5	$61.26	10.187%	$67.5006	$67.50	$67.50	$67.50
Purchase #6	$142.31	4.152%	$148.2187	$148.22	$148.20	$148.20
Purchase #7	$248.67	7.116%	$266.3654	$266.37	$266.35	$266.40
7 purchase totals =	$1,116.82		$1,213.6888	$1,213.69	$1,213.65	$1,213.70