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	$127.96	4.208%	$133.3446	$133.34	$133.35	$133.30
Purchase #2	$101.30	10.417%	$111.8524	$111.85	$111.85	$111.90
Purchase #3	$228.83	13.553%	$259.8433	$259.84	$259.85	$259.80
Purchase #4	$64.32	9.351%	$70.3346	$70.33	$70.35	$70.30
Purchase #5	$204.69	6.720%	$218.4452	$218.45	$218.45	$218.40
Purchase #6	$142.25	7.726%	$153.2402	$153.24	$153.25	$153.20
Purchase #7	$150.25	6.460%	$159.9562	$159.96	$159.95	$160.00
7 purchase totals =	$1,019.60		$1,107.0165	$1,107.01	$1,107.05	$1,106.90