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	$47.98	11.493%	$53.4943	$53.49	$53.50	$53.50
Purchase #2	$137.74	6.366%	$146.5085	$146.51	$146.50	$146.50
Purchase #3	$143.46	12.293%	$161.0955	$161.10	$161.10	$161.10
Purchase #4	$87.86	7.136%	$94.1297	$94.13	$94.15	$94.10
Purchase #5	$102.58	8.675%	$111.4788	$111.48	$111.50	$111.50
Purchase #6	$192.78	10.168%	$212.3819	$212.38	$212.40	$212.40
Purchase #7	$46.69	9.497%	$51.1241	$51.12	$51.10	$51.10
7 purchase totals =	$759.09		$830.2128	$830.21	$830.25	$830.20