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	$91.39	9.592%	$100.1561	$100.16	$100.15	$100.20
Purchase #2	$50.70	5.181%	$53.3268	$53.33	$53.35	$53.30
Purchase #3	$164.99	10.316%	$182.0104	$182.01	$182.00	$182.00
Purchase #4	$122.48	3.300%	$126.5218	$126.52	$126.50	$126.50
Purchase #5	$74.67	11.415%	$83.1936	$83.19	$83.20	$83.20
Purchase #6	$162.40	6.267%	$172.5776	$172.58	$172.60	$172.60
Purchase #7	$140.53	7.549%	$151.1386	$151.14	$151.15	$151.10
7 purchase totals =	$807.16		$868.9249	$868.93	$868.95	$868.90