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	$77.51	7.764%	$83.5279	$83.53	$83.55	$83.50
Purchase #2	$155.30	11.234%	$172.7464	$172.75	$172.75	$172.70
Purchase #3	$36.96	7.467%	$39.7198	$39.72	$39.70	$39.70
Purchase #4	$99.50	11.712%	$111.1534	$111.15	$111.15	$111.20
Purchase #5	$31.91	13.593%	$36.2475	$36.25	$36.25	$36.20
Purchase #6	$176.60	8.749%	$192.0507	$192.05	$192.05	$192.10
Purchase #7	$45.96	4.665%	$48.104	$48.10	$48.10	$48.10
7 purchase totals =	$623.74		$683.5497	$683.55	$683.55	$683.50