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	$45.34	12.129%	$50.8393	$50.84	$50.85	$50.80
Purchase #2	$101.26	10.113%	$111.5004	$111.50	$111.50	$111.50
Purchase #3	$107.71	3.339%	$111.3064	$111.31	$111.30	$111.30
Purchase #4	$97.98	3.604%	$101.5112	$101.51	$101.50	$101.50
Purchase #5	$214.78	7.736%	$231.3954	$231.40	$231.40	$231.40
Purchase #6	$229.81	9.743%	$252.2004	$252.20	$252.20	$252.20
Purchase #7	$128.45	3.547%	$133.0061	$133.01	$133.00	$133.00
7 purchase totals =	$925.33		$991.7592	$991.77	$991.75	$991.70