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	$122.54	12.262%	$137.5659	$137.57	$137.55	$137.60
Purchase #2	$97.81	13.668%	$111.1787	$111.18	$111.20	$111.20
Purchase #3	$233.89	13.871%	$266.3329	$266.33	$266.35	$266.30
Purchase #4	$169.92	11.762%	$189.906	$189.91	$189.90	$189.90
Purchase #5	$121.32	4.317%	$126.5574	$126.56	$126.55	$126.60
Purchase #6	$38.41	5.651%	$40.5805	$40.58	$40.60	$40.60
Purchase #7	$92.85	9.328%	$101.511	$101.51	$101.50	$101.50
7 purchase totals =	$876.74		$973.6324	$973.64	$973.65	$973.70