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	$30.75	5.135%	$32.329	$32.33	$32.35	$32.30
Purchase #2	$145.67	5.788%	$154.1014	$154.10	$154.10	$154.10
Purchase #3	$126.64	8.721%	$137.6843	$137.68	$137.70	$137.70
Purchase #4	$82.52	9.870%	$90.6647	$90.66	$90.65	$90.70
Purchase #5	$101.29	10.511%	$111.9366	$111.94	$111.95	$111.90
Purchase #6	$242.75	6.215%	$257.8369	$257.84	$257.85	$257.80
Purchase #7	$205.51	7.205%	$220.317	$220.32	$220.30	$220.30
7 purchase totals =	$935.13		$1,004.8699	$1,004.87	$1,004.90	$1,004.80